Try using gnostic's openAPI v3 generation

[tstirrat15]

See here: https://github.com/google/gnostic/tree/main/cmd/protoc-gen-openapi

It appears to be abandonware, but the current lib we're using doesn't look like it'll ever support openapiv3, which is where most of the generation tooling is headed.

This could give us better bearer token authorization and futureproofs us a little bit (a little bit).