bzlmod version requires protoc 4.X and above

[jduan]

Description

Hi,

I believe rules_proto_grpc uses toolchains_protoc to generate code that corresponds to proto version 4.X and above.

While proto 4.X has been out since Q1 2024 (see https://protobuf.dev/support/version-support/#java), many open source libraries haven't adopted 4.X yet. For example, even some Google libraries are still only working with proto 3.X.

For example, com.google.cloud:google-cloud-dlp still only works with proto-buf 3.X. I believe many other libraries from "com.google.cloud" are the same.

Is it possible to publish a version of "rules_proto_grpc" that works with protobuf 3.X? It's probably a big ask. But it's a practical ask 😄

PS: I'm trying to adopt bzlmod and our large code base is still mostly working with proto 3.X at this point.