Migration of astrohack Data File classes to use Xarray datatrees

[vsmagalhaes]

This migration would follow the steps below:

1. Create a base class that holds general functionality:
   • __init__
   • __setitem__, __getitem__
   • open, is_open, close
   • save? (this would be a way to save an edited datatree to disk convenient for developers, and to group data reduced separately)
   • keys
   • summary
   • observation_summary? probably!
2. Migrate AstrohackBeamcutFile as it is already using data trees.
3. Migrate locit and position files as they are the simplest data structures.
4. Migrate image and panel file, these are the intermediate complexity case.
5. Migrate combine to use the new datastructures.
6. Migrate pointing files these one should be easier.
7. Migrate holog files, these should present a higher level of complexity due to all metadata needed.
   • Here metadata should be simplified, e.g. holog_obs_json should become an attribute of root rather than a separate file on disk.
   • Here we might take this chance to improve extract_holog interface, by adding a easier way to specify that we only want to reduce some antennas.
8. Fix tests and re-enable combine tests
9. Add tests on mds files
10. upload data products for new tests
11. Write an importing routine to migrate old school files to the new format (probably best if possible to be invisible to the user)
12. Cleanup of obsolete code