Ability to whitelist LuaPlayer::connect_to_server() servers

[Ultros]

Firstly, thanks for the implementation! This will make server-hopping much more interesting in multi-map scenarios such as Clusterio.

I would like to request an improvement to this command, specifically the ability to whitelist servers from this list. While the prompt is important to avoid potential attacks from map owners forcing connects without players' permission, it can also get tedious when there's a need to switch between servers frequently. Allowing whitelists of specific servers (for example with a default unchecked checkbox when first connecting) would alleviate this problem.

[mrudat]

Alternatively, could a notion of a cluster be added; if you connect to a server that's part of a cluster, it allows transfer to other nodes in that cluster.