openapiv3: Support SecurityDefinitions and SecurityRequirement equivalents

Feature

I'm working on converting a person project over to openapiv3. I currently make use of SecurityDefinitions and SecurityRequirement in the old grpc.gateway.protoc_gen_openapiv2.options.openapiv2_swagger as part of my Swagger UI integration. Having the v3 equivalents would be helpful.

May be relevant: https://spec.openapis.org/oas/v3.1.0#security-scheme-object https://spec.openapis.org/oas/v3.1.0#security-requirement-object

Thank you.