feat: added userCount and containsConnection methods to UserManager

Server/src/main/java/uulm/teamname/marvelous/server/netconnector/UserManager.java

@@ -265,4 +265,13 @@ public class UserManager {
 
         client.socket.close(CloseFrame.NORMAL);
     }
+
+
+    public int getUserCount() {
+        return clients.size();
+    }
+
+    public boolean containsConnection(WebSocket conn) {
+        return clients.containsKey(conn);
+    }
 }