protoc-gen-go-grpc support split single proto file gen to diffrent package

[qianlongzt]

Use case(s) - what problem will this feature solve?

opentelemetry-go1 supports protobuf over gRPC and over HTTP, but its proto file defines both the service and related messages in the same file.
When using protobuf over HTTP, it's necessary to remove the gRPC dependency to reduce the binary size.

Proposed Solution

Add an option to rename grpc file.GoImportPath 5

-	g := gen.NewGeneratedFile(filename, file.GoImportPath)
+	path := file.GoImportPath
+ 	if n, ok := rename[file.Desc.Path()]; ok {
+ 		path = n
+	}
+	g := gen.NewGeneratedFile(filename, path)

-grpc_rename log.proto=github.com/aaa/bbb/xxx -grpc_rename trace.proto=github.com/aaa/bbb/yyy

Alternatives Considered

1. opentelemetry-proto split proto file
2. opentelemetry-proto-go add same shim file Feat split grpc again open-telemetry/opentelemetry-proto-go#248

Additional Context

open-telemetry/opentelemetry-go#2579

[arjan-bal]

Hi @qianlongzt, I was going though the linked issue but I don't completely understand how the proposed change addresses the issue. I found this comment that summarises the change: open-telemetry/opentelemetry-go#2579 (comment)

Can you elaborate how your proposed solution will solve the problem of splitting gRPC client/server code and protobuf request/response messages into two separate packages?

[qianlongzt]

@arjan-bal #8245 I created a pr.