Further tooling: black, flake8, and precommit-hooks

[SebastianSchmidl]

Improve the code quality of this project and make contributing easier by adding the following tools to our process and CI:

• black (automatic file formatting)
• flake8 (Python linting)
• pre-commit (run hooks on every commit)

We additionally include flake8 in the CI to ensure proper code quality before merging or building a package.

---

Most changes in this PR are from the tools. See individual commits for better review.

[codecov]

Codecov Report

Merging #32 (d393ccf) into main (6834ec8) will increase coverage by 0.12%.
The diff coverage is 82.95%.

@@            Coverage Diff             @@
##             main      #32      +/-   ##
==========================================
+ Coverage   89.87%   89.99%   +0.12%     
==========================================
  Files          53       53              
  Lines        2083     2088       +5     
==========================================
+ Hits         1872     1879       +7     
+ Misses        211      209       -2     

Flag	Coverage Δ
unittests	89.99% <82.95%> (+0.12%)	⬆️

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Impacted Files	Coverage Δ
gutenTAG/anomalies/types/frequency.py	96.42% <0.00%> (ø)
gutenTAG/anomalies/types/platform.py	92.30% <0.00%> (ø)
gutenTAG/api/__init__.py	0.00% <0.00%> (ø)
gutenTAG/config/schema_loader.py	100.00% <ø> (ø)
gutenTAG/utils/compatibility.py	75.00% <ø> (ø)
gutenTAG/utils/default_values.py	100.00% <ø> (ø)
gutenTAG/utils/global_variables.py	100.00% <ø> (ø)
gutenTAG/utils/logger.py	87.50% <0.00%> (+14.77%)	⬆️
gutenTAG/anomalies/types/mode_correlation.py	91.30% <33.33%> (ø)
gutenTAG/anomalies/types/mean.py	92.85% <50.00%> (ø)
... and 34 more

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