py_proto_library should now come from protobuf

[dws]

Per https://protobuf.dev/news/2024-10-01/ the protobuf repo will be the source of the py_proto_library rule.
This ticket covers updating xds to load py_proto_library from protobuf instead of grpc.

[adisuissa]

cc @phlax
Was this addressed in the Envoy repo? I want to make sure that we are aligned on the same solution for both repos.

[phlax]

see envoyproxy/envoy#40104 (comment)

[adisuissa]

see envoyproxy/envoy#40104 (comment)

Almost at the same time :)
I'll try to see if I can get a few PRs for this migration in the next few days.