Multiple override files for settings #2
Description
The server can currently handle a single settings file via the -s/--settings-file option. However, some settings need to be defined for all installations of future-mobility, some are needed for a particular mod (e.g. the theme) and some are only relevant for a particular installation (e.g. the gridOverlay). Being able to handle these layers separately would simplify the software setup quite a bit, make switching between different mods easier (when running on the same hardware) and would be less error prone since an update in the upstream settings.yml would not require updating a locally modified settings.yml (which would be stored elsewhere in the filesystem to not be overwritten by an update).