Use valid HI source catalogs, improve catalog access methods

[lmachadopolettivalle]

• Remove SOUTH_CATALOG_FACTOR parameter, and instead rely on correct source catalogs
• Use updated HI source catalog with corrected 21cm flux values
• Deprecate old catalogs with incorrect flux values
• Move away from methods that are too specific, and rely on general file access methods instead

[codecov[bot]]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (287142e) 74.96% compared to head (4d746d5) 75.00%.

Files	Patch %	Lines
karabo/simulation/sky_model.py	83.33%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #527 +/- ## ========================================== + Coverage 74.96% 75.00% +0.03% ========================================== Files 35 35 Lines 3859 3836 -23 ========================================== - Hits 2893 2877 -16 + Misses 966 959 -7 ```

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