Add service proto file

Author: AdrienVannson

tests/inputs/simple_service/simple_service.proto

@@ -0,0 +1,21 @@
+syntax = "proto3";
+
+package simple_service;
+
+message Request {
+    int32 value = 1;
+}
+
+message Response {
+    string message = 1;
+}
+
+service SimpleService {
+    rpc GetUnaryUnary (Request) returns (Response);
+
+    rpc GetUnaryStream (Request) returns (stream Response);
+
+    rpc GetStreamUnary (stream Request) returns (Response);
+
+    rpc GetStreamStream (stream Request) returns (stream Response);
+}