This is my Kotlin Spring implementation of @cachescrubber's excellent work in #11258 and #11531.

A user can now select a Documentation Provider (None, Source, Springfox, Springdoc), an Annotation Library (None, Swagger1, Swagger2) and whether to use Swagger UI.

Please note that this removes the swaggerAnnotations option that previously existed! Considering this, it is probably a good idea to include this PR in version 6.0.0 with breaking changes, if the PR is deemed to be useful and of sufficient quality.

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/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.
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

@cachescrubber @wing328 @jimschubert @dr4ke616 @karismann @Zomzog @andrewemery @4brunu @yutaka0m