Add protovalidate as alternative to protoc-gen-validate

[tstirrat15]

Description

I ran into this while looking into authzed-rb's implementation of validation. I hoped that it might solve that problem, but it turns out that there isn't a protovalidate implementation for ruby either (yet, I hope).

I think there's still value in bringing this in, though.

protoc-gen-validate is in maintenance mode: https://github.com/bufbuild/protoc-gen-validate?tab=readme-ov-file#-protoc-gen-validate-pgv

The library they want us to move to is protovalidate: https://github.com/bufbuild/protovalidate

This follows the steps in the migration guide to add annotations that are compatible with protovalidate and allow the downstream libs to use the protovalidate libs as desired.

Notes

The breaking change lint step is complaining, but I ran it locally and it's not code that we use directly or control:

➜  api git:(use-protovalidate-instead-of-protoc-gen-validate) buf breaking . --against https://github.com/authzed/api.git\#branch\=main
protoc-gen-openapiv2/options/openapiv2.proto:45:1:Previously present reserved range "[13]" on message "Swagger" is missing values: [13] were removed.
protoc-gen-openapiv2/options/openapiv2.proto:587:1:Previously present reserved range "[1]" on message "Tag" is missing values: [1] were removed.

It appears to be complaining about the proto provided by the grpc-gateway dep, and that version bump happened when I added the new dependency. I'm not particularly concerned about it breaking anything.

Changes

• Update buf.yaml to v2
• Run buf format over everything
• Run the migration steps from the protovalidate repo: https://github.com/bufbuild/protovalidate/blob/main/docs/migrate.md

Notes

This does not remove support for protoc-gen-validate. We probably won't do that for a while yet. This should be a non-breaking change.

Testing

Review. See that our CI still passes.