[issue-6080] Fix strict no-$ref-siblings rule violations

[jgreffe]

References to other Issues or PRs

Fixes #6080

Have you read the Contributing Guidelines?

Brief description of what is fixed or changed

Introduce a new option omit_array_item_type_when_ref_sibling which allows to omit a type: object if a $ref already exists.
This fixes strict no-$ref-siblings rule violations.
But default this option is false to keep previous behavior.

Other comments

[jgreffe]

almost the same test as TestArrayMessageItemsType, but we check we don't have results like these.

[johanbrandhorst]

Thanks for this! Could you please add a section to our docs for this new option? https://github.com/grpc-ecosystem/grpc-gateway/blob/main/docs/docs/mapping/customizing_openapi_output.md is usually used for options.

Also, since this is a new option, we need to add support for it to our Bazel definitions. Please see existing patterns for options in https://github.com/grpc-ecosystem/grpc-gateway/blob/main/protoc-gen-openapiv2/defs.bzl and add this option. Thanks!

[johanbrandhorst]

Amazing, thank you!

[johanbrandhorst]

Looks like a minor formatting issue in the bazel file, I would ignore the fuzz error

[johanbrandhorst]

Thanks for your contribution!