feat: add outgoing messages to client

Client/Domain/DTO/OutgoingMessage.cs

@@ -0,0 +1,28 @@
+using Client.Domain.Enums;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Client.Domain.DTO
+{
+    public class OutgoingMessage<T>
+    {
+        public readonly OutgoingMessageTypeEnum Type;
+        public readonly T? Content;
+
+        public OutgoingMessage(OutgoingMessageTypeEnum type, T? content = default)
+        {
+            Type = type;
+            Content = content;
+        }
+    }
+
+    public class EmptyOutgoingMessage : OutgoingMessage<uint>
+    {
+        public EmptyOutgoingMessage(OutgoingMessageTypeEnum type) : base(type)
+        {
+        }
+    }
+}