track private slots for webfront overview

SharedLibraryCore/Interfaces/IGameServer.cs

@@ -73,6 +73,11 @@ namespace SharedLibraryCore.Interfaces
         /// </summary>
         string GamePassword { get; }
         
+        /// <summary>
+        /// Number of private client slots
+        /// </summary>
+        int PrivateClientSlots { get; }
+        
         /// <summary>
         /// Current map the game server is running
         /// </summary>