Option to ommit auth system for local-only connections

[O1LER]

Currently you need an active internet connection in order to authenticate a player. It would be nice to allow local-only play without the need for an internet connection.

It would be nice to be able to ommit the need for player authentication with the backend, for example trough a start/ENV argument like local, and allowing clients to connect without authentication that have their own local flag set.

This ties into https://github.com/BeamMP/BeamMP-Launcher/issues/173 and https://github.com/BeamMP/BeamMP-Launcher/issues/54