chore(docs): Move CONTRIBUTING.md to top-level (#17744)

And remove the symlink. Contributors continue to be confused by the
top-level file being a symlink
since in the Github UI it appears to be a mostly empty file.

Recent example of confusion:
#17743

Signed-off-by: Jesse Szwedko <[email protected]>

Signed-off-by: Jesse Szwedko <[email protected]>

Author: jszwedko

CONTRIBUTING.md

@@ -0,0 +1,256 @@
+# Contributing
+
+First, thank you for contributing to Vector! The goal of this document is to
+provide everything you need to start contributing to Vector. The
+following TOC is sorted progressively, starting with the basics and
+expanding into more specifics. Everyone from a first time contributor to a
+Vector team member will find this document useful.
+
+- [Introduction](#introduction)
+- [Your First Contribution](#your-first-contribution)
+  - [New sources, sinks, and transforms](#new-sources-sinks-and-transforms)
+- [Workflow](#workflow)
+  - [Git Branches](#git-branches)
+  - [Git Commits](#git-commits)
+    - [Style](#style)
+  - [GitHub Pull Requests](#github-pull-requests)
+    - [Title](#title)
+    - [Reviews & Approvals](#reviews--approvals)
+    - [Merge Style](#merge-style)
+  - [CI](#ci)
+    - [Releasing](#releasing)
+    - [Testing](#testing)
+      - [Skipping tests](#skipping-tests)
+      - [Daily tests](#daily-tests)
+    - [Flakey tests](#flakey-tests)
+      - [Test harness](#test-harness)
+  - [Deprecations](#deprecations)
+  - [Dependencies](#dependencies)
+- [Next steps](#next-steps)
+- [Legal](#legal)
+  - [Contributor License Agreement](#contributor-license-agreement)
+  - [Granted rights and copyright assignment](#granted-rights-and-copyright-assignment)
+
+## Introduction
+
+1. **You're familiar with [GitHub](https://github.com) and the pull request
+   workflow.**
+2. **You've read Vector's [docs](https://vector.dev/docs/).**
+3. **You know about the [Vector community](https://vector.dev/community/).
+   Please use this for help.**
+
+## Your First Contribution
+
+1. Ensure your change has an issue! Find an
+   [existing issue][urls.existing_issues] or [open a new issue][urls.new_issue].
+   - This is where you can get a feel if the change will be accepted or not.
+     Changes that are questionable will have a `needs: approval` label.
+2. Once approved, [fork the Vector repository][urls.fork_repo] in your own
+   GitHub account (only applicable to outside contributors).
+3. [Create a new Git branch][urls.create_branch].
+4. Make your changes.
+5. [Submit the branch as a pull request][urls.submit_pr] to the main Vector
+   repo. A Vector team member should comment and/or review your pull request
+   within a few days. Although, depending on the circumstances, it may take
+   longer.
+
+### New sources, sinks, and transforms
+
+If you're thinking of contributing a new source, sink, or transform to Vector, thank you that's way cool! The answers to
+the below questions are required for each newly proposed component and depending on the answers, we may elect to not
+include the proposed component. If you're having trouble with any of the questions, we're available to help you.
+
+**Prior to beginning work on a new source or sink if a GitHub Issue does not already exist, please open one to discuss
+the introduction of the new integration.** Maintainers will review the proposal with the following checklist in mind,
+try and consider them when sharing your proposal to reduce the amount of time it takes to review your proposal. This
+list is not exhaustive, and may be updated over time.
+
+- [ ] Can the proposed component’s functionality be replicated by an existing component, with a specific configuration?
+(ex: Azure Event Hub as a `kafka` sink configuration)
+  - [ ] Alternatively implemented as a wrapper around an existing component. (ex. `axiom` wrapping `elasticsearch`)
+- [ ] Can an existing component replicate the proposed component’s functionality, with non-breaking changes?
+- [ ] Can an existing component be rewritten in a more generic fashion to cover both the existing and proposed functions?
+- [ ] Is the proposed component generically usable or is it specific to a particular service?
+  - [ ] How established is the target of the integration, what is the relative market share of the integrated service?
+- [ ] Is there sufficient demand for the component?
+  - [ ] If the integration can be served with a workaround or more generic component, how painful is this for users?
+- [ ] Is the contribution from an individual or the organization owning the integrated service? (examples of
+organization backed integrations: `databend` sink, `axiom` sink)
+  - [ ] Is the contributor committed to maintaining the integration if it is accepted?
+- [ ] What is the overall complexity of the proposed design of this integration from a technical and functional
+standpoint, and what is the expected ongoing maintenance burden?
+- [ ] How will this integration be tested and QA’d for any changes and fixes?
+  - [ ] Will we have access to an account with the service if the integration is not open source?
+
+To merge a new source, sink, or transform, the pull request is required to:
+
+- [ ] Add tests, especially integration tests if your contribution connects to an external service.
+- [ ] Add instrumentation so folks using your integration can get insight into how it's working and performing. You can
+see some [example of instrumentation in existing integrations](https://github.com/vectordotdev/vector/tree/master/src/internal_events).
+- [ ] Add documentation. You can see [examples in the `docs` directory](https://github.com/vectordotdev/vector/blob/master/docs).
+
+When adding new integration tests, the following changes are needed in the GitHub Workflows:
+
+- in `.github/workflows/integration.yml`, add another entry in the matrix definition for the new integration.
+- in `.github/workflows/integration-comment.yml`, add another entry in the matrix definition for the new integration.
+- in `.github/workflows/changes.yml`, add a new filter definition for files changed, and update the `changes` job
+outputs to reference the filter, and finally update the outputs of `workflow_call` to include the new filter.
+
+## Workflow
+
+### Git Branches
+
+_All_ changes must be made in a branch and submitted as [pull requests](#github-pull-requests).
+Vector does not adopt any type of branch naming style, but please use something
+descriptive of your changes.
+
+### Git Commits
+
+#### Style
+
+Please ensure your commits are small and focused; they should tell a story of
+your change. This helps reviewers to follow your changes, especially for more
+complex changes.
+
+### GitHub Pull Requests
+
+Once your changes are ready you must submit your branch as a [pull request](https://github.com/vectordotdev/vector/pulls).
+
+#### Title
+
+The pull request title must follow the format outlined in the [conventional commits spec](https://www.conventionalcommits.org).
+[Conventional commits](https://www.conventionalcommits.org) is a standardized
+format for commit messages. Vector only requires this format for commits on
+the `master` branch. And because Vector squashes commits before merging
+branches, this means that only the pull request title must conform to this
+format. Vector performs a pull request check to verify the pull request title
+in case you forget.
+
+A list of allowed sub-categories is defined
+[here](https://github.com/vectordotdev/vector/tree/master/.github).
+
+The following are all good examples of pull request titles:
+
+```text
+feat(new sink): new `xyz` sink
+feat(tcp source): add foo bar baz feature
+fix(tcp source): fix foo bar baz bug
+chore: improve build process
+docs: fix typos
+```
+
+#### Reviews & Approvals
+
+All pull requests should be reviewed by:
+
+- No review required for cosmetic changes like whitespace, typos, and spelling
+  by a maintainer
+- One Vector team member for minor changes or trivial changes from contributors
+- Two Vector team members for major changes
+- Three Vector team members for RFCs
+
+If CODEOWNERS are assigned, a review from an individual from each of the sets of owners is required.
+
+#### Merge Style
+
+All pull requests are squashed and merged. We generally discourage large pull
+requests that are over 300-500 lines of diff. If you would like to propose a
+change that is larger we suggest coming onto our [Discord server](https://chat.vector.dev/) and discuss it
+with one of our engineers. This way we can talk through the solution and
+discuss if a change that large is even needed! This will produce a quicker
+response to the change and likely produce code that aligns better with our
+process.
+
+### CI
+
+Currently, Vector uses GitHub Actions to run tests. The workflows are defined in
+`.github/workflows`.
+
+#### Releasing
+
+GitHub Actions is responsible for releasing updated versions of Vector through
+various channels.
+
+#### Testing
+
+##### Skipping tests
+
+Tests are run for all changes except those that have the label:
+
+```text
+ci-condition: skip
+```
+
+##### Daily tests
+
+Some long-running tests are only run daily, rather than on every pull request.
+If needed, an administrator can kick off these tests manually via the button on
+the [nightly build action
+page](https://github.com/vectordotdev/vector/actions?query=workflow%3Anightly)
+
+#### Flakey tests
+
+Historically, we've had some trouble with tests being flakey. If your PR does
+not have passing tests:
+
+- Ensure that the test failures are unrelated to your change
+  - Is it failing on master?
+  - Does it fail if you rerun CI?
+  - Can you reproduce locally?
+- Find or open an issue for the test failure
+  ([example](https://github.com/vectordotdev/vector/issues/3781))
+- Link the PR in the issue for the failing test so that there are more examples
+
+##### Test harness
+
+You can invoke the [test harness][urls.vector_test_harness] by commenting on
+any pull request with:
+
+```bash
+/test -t <name>
+```
+
+### Deprecations
+
+When deprecating functionality in Vector, see [DEPRECATION.md](DEPRECATION.md).
+
+### Dependencies
+
+When adding, modifying, or removing a dependency in Vector you may find that you need to update the
+inventory of third-party licenses maintained in `LICENSE-3rdparty.csv`. This file is generated using
+[rust-license-tool](https://github.com/DataDog/rust-license-tool.git) and can be updated using
+`cargo vdev build licenses`.
+
+## Next steps
+
+As discussed in the [`README`](README.md), you should continue to the following
+documents:
+
+1. **[DEVELOPING.md](DEVELOPING.md)** - Everything necessary to develop
+2. **[DOCUMENTING.md](DOCUMENTING.md)** - Preparing your change for Vector users
+3. **[DEPRECATION.md](DEPRECATION.md)** - Deprecating functionality in Vector
+
+## Legal
+
+To protect all users of Vector, the following legal requirements are made.
+If you have additional questions, please [contact us].
+
+### Contributor License Agreement
+
+Vector requires all contributors to sign the Contributor License Agreement
+(CLA). This gives Vector the right to use your contribution as well as ensuring
+that you own your contributions and can use them for other purposes.
+
+The full text of the CLA can be found at [https://cla.datadoghq.com/vectordotdev/vector](https://cla.datadoghq.com/vectordotdev/vector).
+
+### Granted rights and copyright assignment
+
+This is covered by the CLA.
+
+[contact us]: https://vector.dev/community
+[urls.create_branch]: https://help.github.com/en/github/collaborating-with-issues-and-pull-requests/creating-and-deleting-branches-within-your-repository
+[urls.existing_issues]: https://github.com/vectordotdev/vector/issues
+[urls.fork_repo]: https://help.github.com/en/github/getting-started-with-github/fork-a-repo
+[urls.new_issue]: https://github.com/vectordotdev/vector/issues/new
+[urls.submit_pr]: https://help.github.com/en/github/collaborating-with-issues-and-pull-requests/creating-a-pull-request-from-a-fork
+[urls.vector_test_harness]: https://github.com/vectordotdev/vector-test-harness/