547 hotfix mightee

[Lukas113]

closes #547

This PR addresses the following:

• Reading correct cols from .fits files of MIGHTEE and GLEAM
• Implemented a correct and generalized version to read sky-sources from .fits file. The previous version had the following issues:
  • Didn't consider unit-scaling & checks
  • Didn't allow to read frequencies
  • Was not generalized
• Introduced helper-classes with tests to address these issues

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 94.07666% with 17 lines in your changes are missing coverage. Please review.

Project coverage is 66.86%. Comparing base (9e2b77c) to head (ef59de9).

Files	Patch %	Lines
karabo/simulation/sky_model.py	94.03%	17 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #560 +/- ## ========================================== + Coverage 65.96% 66.86% +0.89% ========================================== Files 49 49 Lines 4792 4970 +178 ========================================== + Hits 3161 3323 +162 - Misses 1631 1647 +16 ```

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