[jaxrs-spec] Add @Generated annotation to enums

[amaechler]

This PR adds a generated (@Generated) annotation to enum classes for the jaxrs-spec generator (A similar addition exists also for the Spring generator here.

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 || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  (For Windows users, please run the script in WSL)
  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.x.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
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Related

• Mark generated classes with annotation: spring and java generators #16145, but it doesn't include jaxrs and includes much broader changes

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Summary by cubic

Adds @generated to JAX-RS Spec–generated enum classes so tools can recognize generated code and reduce warning noise. Aligns JAX-RS Spec with the Spring generator behavior.

• New Features
  • Added {{>generatedAnnotation}} to enumOuterClass.mustache to annotate all generated enums.
  • Emits javax.annotation.Generated or jakarta.annotation.Generated based on the variant.
  • Updated all jaxrs-spec petstore samples to include the annotation.

^{Written for commit 1098976. Summary will update on new commits.}

[cubic-dev-ai]

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