feat: add quiet mode to suppress verbose generation output (#11211)

[saxicek]

Implement a --quiet / -q flag to suppress donation banners and contributor messages during code generation. This addresses issue #11211 by providing users a way to reduce noisy console output while maintaining full generation semantics.

Changes:

• Add quiet mode configuration to WorkflowSettings (core module)
• Wire quiet setting through CodegenConfigurator
• Implement CLI option: -q, --quiet in Generate command
• Add Maven plugin parameter: <quiet>true</quiet>
• Add Gradle extension property: openApiGenerator.quiet = true
• Refactor postProcess() in DefaultCodegen and 19 language generators to wrap println statements with if (!isQuietMode()) guard, ensuring all other lifecycle activities execute normally regardless of quiet mode
• Add GlobalSettings lookup utility isQuietMode() to language-specific codegen
• Update documentation for usage.md, Maven plugin README, Gradle plugin README
• Add comprehensive test coverage across all modules:
  • WorkflowSettingsTest: quiet setting serialization
  • GenerateTest: CLI quiet flag parsing
  • DefaultGeneratorTest: postProcess execution verification
  • GenerateTaskDslTest: Gradle quiet output suppression
  • CodeGenMojoTest: Maven plugin quiet behavior

Verification:

• DefaultGeneratorTest: 24 tests, 0 failures
• GenerateTaskDslTest: all tests pass
• Build: EXIT 0

This implementation maintains backward compatibility (quiet defaults to false) and ensures semantic correctness by always invoking postProcess(), affecting only the console output suppression behavior.

Closes #11211

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---

Summary by cubic

Adds a quiet mode to suppress donation and contributor banners during generation across CLI, Maven, and Gradle. Behavior is unchanged; postProcess still runs and quiet defaults to false.

• New Features

  • CLI: -q, --quiet
  • Maven: <quiet>true</quiet> or openapi.generator.maven.plugin.quiet
  • Gradle: openApiGenerate.quiet = true
  • Core: WorkflowSettings and CodegenConfigurator#setQuiet, propagated via GlobalSettings
  • Docs and tests updated for CLI, Gradle, Maven, and generator lifecycle

• Refactors

  • Wrapped banner prints in DefaultCodegen and 19 language generators with if (!isQuietMode())
  • Added isQuietMode() helper to read the quiet global setting

^{Written for commit 91c816e. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 36 files

_{Re-trigger cubic}

[wing328]

thanks for contributing this enhancement.

i'll review and let you know if i've any question or feedback.

[saxicek]

Rebased my commit on the current master branch.

[saxicek]

@wing328 Sorry to disturb, do you think you can check this anytime soon? Or shall I mention someone else to have a look? Thank you!

[wing328]

let me try to review and get this merged this weekend.

thanks again for the PR

have a nice weekend.

[wing328]

tested locally and worked as expected to suppress donation messages.

but later users may have feedback on what "quiet mode" means.

some other commands have quiet mode that suppresses even error messages while others only suppress "typical output" (INFO by the logger) for example.

we may need to further revise it after shipping it to our users.