Github issue template for new checkers

[terriko]

It would be nice if we have a checklist/template available for folks contributing a new checker so they don't miss any common steps.

[BreadGenie]

Something like in #1296 is what I had in mind.

[XDRAGON2002]

I think we should have PR templates for checker additions as well as non-checker issues.

As a lot of the currently open issues are checker related and will only increase in the future, having a separate checklist PR for checkers could prove to be fruitful.
As suggested by @BreadGenie it could look like #1296 (maybe adding a few extra checklist marks like added filename pattern, version pattern, product version pattern could also be helpful).

In regards to the non-checker based PRs they could be a standard checklist consisting of checks for all formatters, issue number that the PR fixes and a brief description of the changes (this would allow reviewers to get a gist of the changes without going through the entire code changes just to understand what the PR tries to resolve and how)

Moreover these checklist formats for PR would also serve as a reminder to contributors for the steps to be followed.