feat: Add BungeeGuard Compatible mode

[kubo6472]

Like Velocity 3.x, add mode where it will still support 1.7-1.19.x but use the token for something like BungeeGuard.

[robinbraemer]

Are you using BungeeGuard?

[kubo6472]

Yes, I was using it with velocity. Wanted to do some testing with gate. As velocity has almost, if not larger memory consumption than a full minecraft server. Truth be told, I'm "hosting" an auth server directly from proxy, using LimboAPI velocity plugin, but still, I tried it without all of that and it still has enormous memory footprint. With versions below 1.13.x I will have to use something like bungeeguard instead of the modern velocity style forwarding.