Draft: Rework Repo

1. Rename astronaut-analysis.py to astronaut_analysis.py so it can be imported properly.
2. Improve .gitlab-ci in order to test against python 3.9 up to python 3.11.
3. Add pytest and wrap it inside acceptance-test.sh. Fix various datetime related errors in astronaut_analysis.py.
4. Add CITATION.cff. Update package versions in requirements.txt.
5. Add requirements for tests and CI/CD in separate requirement files.
6. Add VERSION.txt, so versioning of this package can be handled bettter.

Todo

Apply Internal Contributions as defined in CONTRIBUTING.md

Solves #7