Allow repo mods to be downloaded by the server

[PolygonError]

Is your feature request related to a problem? Please describe.
No

Describe the solution you'd like
A user can define a list of mod IDs from the BeamNG repo in the server config, which at boot the server would download automatically.
If the mod is already downloaded, at server launch it will check for updates and download/replace automatically.

Example of ServerConfig.toml:

[General]
# Unique ID for 'Sierra Summit Raceway' and 'Turbo Everything + Twincharge Everything'
RepoMods = ["MUJD7KO56", "M3YSALXWH"]