Add system to kick people if they connect to multiple servers at once. (#34563)

Content.Server/Database/ServerDbBase.cs

@@ -1801,6 +1801,8 @@ INSERT INTO player_round (players_id, rounds_id) VALUES ({players[player]}, {id}
 
         #endregion
 
+        public abstract Task SendNotification(DatabaseNotification notification);
+
         // SQLite returns DateTime as Kind=Unspecified, Npgsql actually knows for sure it's Kind=Utc.
         // Normalize DateTimes here so they're always Utc. Thanks.
         protected abstract DateTime NormalizeDatabaseTime(DateTime time);