Fix the Fortran code documentaion

[eirikurj]

Purpose

Noticed that the Fortran code documentation was broken.

This PR

• adds a static html path such that the Doxygen code documentation is copied over
• removes a redundant css that is provided by the sphinx_mdolab_theme.
• Updates the Doxygen config file to support version 1.9, which is consistent with that is used on readthedocs.com

Expected time until merged

No rush.

Type of change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (non-backwards-compatible fix or feature)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Documentation update
• Maintenance update
• Other (please describe)

Testing

Checklist

• I have run ruff check and ruff format to make sure the Python code adheres to PEP-8 and is consistently formatted
• I have formatted the Fortran code with fprettify or C/C++ code with clang-format as applicable
• I have run unit and regression tests which pass locally with my changes
• I have added new tests that prove my fix is effective or that my feature works
• I have added necessary documentation

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 41.21%. Comparing base (b1ca667) to head (e79d460).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #395   +/-   ##
=======================================
  Coverage   41.21%   41.21%           
=======================================
  Files          13       13           
  Lines        4125     4125           
=======================================
  Hits         1700     1700           
  Misses       2425     2425           

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