Telescope Class: Accept OSKAR and RASCIL backends

[lmachadopolettivalle]

Implement changes described in #421 for the Telescope Class.

• Introduce a backend class via the SimulatorBackend enum
• Accept RASCIL as a backend to obtain its Telescope objects
• Modify how users can obtain a Telescope instance. Now, users can call e.g. Telescope.constructor("MeerKAT") instead of the more hard-coded Telescope.get_MEERKAT_Telescope()
• Modify plot_telescope to take into account which backend is being used
• Modify tests to use the new constructor method

[Lukas113]

Another note:

You have used a Python3.10 type-annotation feature. To do a Union with | is just allowed from Python3.10, and we're operating on Python3.9 at the moment. The reason why Pylance is not complaining is because there is a from __future__ import annotations at the start of the file. However, it's still not a valid operator in Python3.9. That's the reason why mypy is complaining.

[codecov[bot]]

Codecov Report

Attention: 17 lines in your changes are missing coverage. Please review.

Comparison is base (2bb1733) 74.04% compared to head (a003ca1) 73.16%.

Files	Patch %	Lines
karabo/simulation/telescope.py	76.71%	17 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #522 +/- ## ========================================== - Coverage 74.04% 73.16% -0.88% ========================================== Files 34 35 +1 Lines 3614 3652 +38 ========================================== - Hits 2676 2672 -4 - Misses 938 980 +42 ```

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