Add a warning when joining on 1.21.10 and below

At least in my experience, the resource pack for RPG does not load on 1.21.10 (and likely all lower versions). I tried going to Oakhaven and the custom mobs look very weird lol I think it would be good if there was a warning that you are joining on an unsupported version. Perhaps something along the lines of "WARNING: You are joining on an unsupported version. It is highly recommended to join with 1.21.11 for the best experience" I'm fairly sure this should be detectable server side (what version the client is), especially as you can't even join on outdated versions on a vanilla server