Idea plugin for marking source directories, and omitting gradle wrapper

[anttikarhu]

Idea plugin for marking source directories, and omitting gradle wrapper to enable one to use the generated project as a sub project.
#12500

@jimschubert @dr4ke616 @karismann @Zomzog @andrewemery @4brunu @yutaka0m

PR checklist

• [ x] Read the contribution guidelines.
• [ x] 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.
• [x ] Run the following to build the project and update samples:

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

  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*.
  For Windows users, please run the script in Git BASH.
• [ x] File the PR against the correct branch: master (6.0.1) (patch release), 6.1.x (breaking changes with fallbacks), 7.0.x (breaking changes without fallbacks)
• [ x] If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

[4brunu]

Hey, first of all, thanks for creating this PR.

Could you please run the following commands?

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

Thanks

[4brunu]

@anttikarhu could you please create an option to the idea option so that it appears in the docs? Thanks

[4brunu]

Looks good to me 👍