Support Connect RPC with connect-go

[XSAM]

I want to use Connect RPC in my bazel project, but there is no support for it, as the protoc-gen-connect-go expects a subfolder to write when generating go codes.

I am not familiar with bazel, but I wonder if it is possible to generate a subfolder inside the importpath of go_proto_library . So, the generated folder path in bazel keeps consistent with the one from buf.

Having a different output path is a terrible user experience when switching local buf to bazel, as it changes the import path of ConnectRPC.

Originally posted by @XSAM in connectrpc/connect-go#310 (comment)

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In principle rules_go could implement support for proto plugins generating code in subpackages

connectrpc/connect-go#310 (comment)