Docs: Select color scheme based on system preference

[p-rogalski]

Pull Request Checklist

• A news fragment is added in news/ describing what is new.
• Test cases added for changed code.

Describe what you have changed in this PR.

Added a toggle to select the documentation color scheme based on system preference. Additionally, the icons for light and dark mode were adjusted to match the automatic toggle icon.

Related mkdocs documentation: https://squidfunk.github.io/mkdocs-material/setup/changing-the-colors/#automatic-light-dark-mode

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.23%. Comparing base (625e2a5) to head (9c9a049).
⚠️ Report is 52 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3591      +/-   ##
==========================================
- Coverage   85.47%   85.23%   -0.24%     
==========================================
  Files         118      118              
  Lines       12017    12017              
  Branches     1961     1961              
==========================================
- Hits        10271    10243      -28     
- Misses       1180     1209      +29     
+ Partials      566      565       -1     

Flag	Coverage Δ
unittests	85.09% <ø> (-0.23%)	⬇️

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