Add Lua function to get a player's role

[WiserTixx]

Adds MP.GetPlayerRole(player_id) to the Lua API to get a player's role ("USER", "EA", "MDEV", "STAFF", "ET") by their player id. Currently you can only get someone's role in onPlayerAuth from the parameters and in onVehicleSpawned and onVehicleEdited from the packet data, but not in onPlayerJoin for example without storing it.