feat: added user gRPC service

JOBot.Backend/Program.cs

@@ -1,6 +1,9 @@
 var builder = WebApplication.CreateBuilder(args);
+
+builder.Services.AddGrpc();
+
 var app = builder.Build();
 
-app.MapGet("/", () => "Hello World!");
+app.MapGrpcService<UserService>();
 
-app.Run();
+app.Run();