feat: Support for multiple rpc service generation and rpc grouping (#1972)

* Add group & compatible flag

* Add group & compatible flag

* Support for multiple rpc service generation and rpc grouping

* Support for multiple rpc service generation and rpc grouping

* Format code

* Format code

* Add comments

* Fix unit test

* Refactor function name

* Add example & Update grpc readme

* go mod tidy

* update mod

* update mod

tools/goctl/example/rpc/hello.proto

@@ -0,0 +1,17 @@
+syntax = "proto3";
+
+package hello;
+
+option go_package = "./hello";
+
+message HelloReq {
+  string in = 1;
+}
+
+message HelloResp {
+  string msg = 1;
+}
+
+service Greet {
+  rpc SayHello(HelloReq) returns (HelloResp);
+}