Support --incompatible_enable_proto_toolchain_resolution

[kusaeva]

Is your feature request related to a problem?

The problem is need to compile protoc instead of using prebuilt binary while building java_grpc_library

Describe the solution you'd like

Support --incompatible_enable_proto_toolchain_resolution bazel flag so users can override protoc compiled from sources with prebuilt binary, as already done in rules_python or WIP in rules_go

Describe alternatives you've considered

Additional context

Examples of declarations toolchains for other languages that already support the feature here

[kannanjgithub]

Feel free to raise a PR for this.