Geometry parts configuration

[ManuelHu]

We will need a better way to express which parts of the geometry the tool will create. The current approach using --assemblies=strings,fibers,... is too limited.

A list of things that might need to be expressed in the new format/functionality (no particular order, certainly not exhaustive):

• deployment of IB/OB fiber modules (all or only selected) - do we really want this, or should we use custom channelmaps?
• Position of sources in the SIS reference system, deployment of sources
• a timestamp to use for the channelmaps from https://github.com/legend-exp/legend-hardware-config

what will not be part of this file:

• anything that is already present in the metadata

[ManuelHu]

The most important things are already implemented (i.e. the config of calibration sources), and selecting a metadata timestamp is also possible via config.

We should decide, if we want to mirror some CLI flags also to the config file (i.e. fiber model selection, detailed or segmented?)