We are using buf and options to customize final openapi artefact:

• https://github.com/google/gnostic/tree/main/openapiv3
• and we are using it via buf - https://buf.build/search?query=gnostic&type=repository
• and actual documentation for gnostic/gnostic - https://buf.build/gnostic/gnostic

The plugin to build final yamls:

• https://github.com/sudorandom/protoc-gen-connect-openapi

To manage plugins we are using bingo:

• https://github.com/bwplotka/bingo