feat: implement gRPC Greeter service with example proto and enhance makefile

generated/GRPC/Greeter/GreeterInterface.php

@@ -0,0 +1,22 @@
+<?php
+# Generated by the protocol buffer compiler (roadrunner-server/grpc). DO NOT EDIT!
+# source: protos/example.proto
+
+namespace GRPC\Greeter;
+
+use Spiral\RoadRunner\GRPC;
+
+interface GreeterInterface extends GRPC\ServiceInterface
+{
+    // GRPC specific service name.
+    public const NAME = "helloworld.Greeter";
+
+    /**
+    * @param GRPC\ContextInterface $ctx
+    * @param HelloRequest $in
+    * @return HelloReply
+    *
+    * @throws GRPC\Exception\InvokeException
+    */
+    public function SayHello(GRPC\ContextInterface $ctx, HelloRequest $in): HelloReply;
+}