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

PR checklist

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Summary by cubic

Adds a quiet mode to suppress donation and contributor banners during generation, available via 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 across CLI, Gradle, Maven, and generator lifecycle

• Refactors

  • Wrapped banner prints in DefaultCodegen and language generators with if (!isQuietMode())
  • Added isQuietMode() helper; ensured postProcess() always executes

^{Written for commit daadd46. Summary will update on new commits. Review in cubic}

[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.