[Feature] Recognization of proxy commands in server-side (command block, etc.)

[NightLunya]

A clear description of the feature you'd like to see implemented

Following a discussion from Discord:
Enable support of the proxy commands but server-side, so it can be used via command blocks, or plugins/mods which uses signs, buttons or entities/NPCs to execute commands.
Mainly useful to setup fancier ways to teleport players to other servers for example (instead of just typing "/server servername" or "/send player servername") but I think this implementation would be great in the future in case Catalyst grows with more commands.
Maybe use existing Anvil plugin for Spigot (or other server type) to enable this feature, or make a new bridge plugin.

[jacoballen1]

This is something we will have to re-visit when AnvilNet is released (AnvilNet is going to be a major change in the api, Anvil, that will allow us to develop this in a more platform-independent way)