From pdoc to mkdocs (to sphinx)

[veenstrajelmer]

• https://github.com/Deltares/HYDROLIB-core/blob/main/mkdocs.yml
• https://deltares.github.io/HYDROLIB-core/0.5.2/
• https://www.mkdocs.org/user-guide/configuration/
• https://www.mkdocs.org/user-guide/deploying-your-docs/

TODO:

• remove old docgeneration actions (incl PAT)
• add installation+issues to howto
• cleanup readme further and put here instead
• Comment deprecated(?)+errors+linebuilder+modelbuilder in api_reference.md
• remove admonition?
• add link to https://deltares.github.io/xugrid/user_guide.html in tutorials introduction and also point to xarray 45 minutes docs
• "also create unittests" to "also create function docstrings and unittests"
• check mkdocs warnings
• rename tutorials/tutorials to tutorials/introduction
• expand mkdocs with more ipynb files
• include download link for notebooks in docs #776
• modelbuilder notebook is already integrated, but no heading is visible under tutorials
• check TODO and commented lines in mkdocs.yml >> not relevant anymore with sphinx
• exclude many funtions from API reference, add structure to toc and exclude parameters/returns from toc
• move to sphinx, just like ddlpy, although including notebooks is an issue there >> it worked in hatyan with choco install pandoc
• update workflow file
• update pyproject.toml dependencies for sphinx