feat: add interceptor for bufbuild/protovalidate

[gvencadze]

Interceptor for validating incoming requests using bufbuild/protovalidate with Google's Common Expression Language (CEL) support (+ legacy protoc-gen-validate)

Changes

1. Add interceptor that validates incoming requests using bufbuild/protovalidate-go under the hood
2. For unit-testing purposes I've added new proto contract that uses annotations from protovalidate, because it doesn't generate Validate() interface, so I can't reuse already existing contract and codegen
3. Add protovalidate to buf.yaml as depedency, I've tried to use it as local, but without any success. (If usage of protoc for codegen is important, I'll rework this moment)

Verification

I've created sample project, with some proto APIs and check both modes of protovalidate - legacy (like in protoc-gen-validate) and new powered by Google's Common Expression Language (CEL)

I've added examples only for new mode

[johanbrandhorst]

Thanks for this, this is great!

[johanbrandhorst]

Perfect, thanks a lot for this :)

[johanbrandhorst]

The lint error seems to imply we need to rerun the generation script?

https://github.com/grpc-ecosystem/go-grpc-middleware/actions/runs/5872315640/job/15923608916?pr=614

[johanbrandhorst]

Thanks for your contribution!

[akshayjshah]

@johanbrandhorst and @gvencadze - awesome to see this has already landed! Are you open to a follow-up PR that adds an unimplemented Option interface to this package, so that the two exported constructors have some room to evolve without breaking back-compat?

[johanbrandhorst]

Sounds reasonable, this hasn't hit a released version yet.