Add dotnet7 workflow, new samples

[wing328]

• Add dotnet7 workflow
• Add new samples

cc @mandrean (2017/08) @shibayan (2020/02) @Blackclaws (2021/03) @lucamazzanti (2021/05) @iBicha (2023/07)

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh ./bin/configs/*.yaml
  ./bin/utils/export_docs_generators.sh
  

  (For Windows users, please run the script in Git BASH)
  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples as manually written tests may be removed.
• File the PR against the correct branch: master (upcoming 7.1.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

[devhl-labs]

You can use one workflow. The dotnet version property can be an array. https://github.com/actions/setup-dotnet

`yaml
steps:

• uses: actions/checkout@v3
• name: Setup dotnet
  uses: actions/setup-dotnet@v3
  with:
  dotnet-version: |
  3.1.x
  5.0.x
• run: dotnet build
  `

[wing328]

You can use one workflow.

We did that before with java (e.g. JDK11, JDK17, etc) but later there are features only available in latest version (e.g. JDK17) so we end up splitting the workflow based on versions.

[devhl-labs]

Consider renaming these workflows like samples-dotnet8.yaml and then moving aspnet servers to samples-dotnet6

[devhl-labs]

In each workflow, we only need to test the samples which target that framework, so this file only needs .net 6 samples.

[wing328]

right, will do