Automatically build PDF documentation

[JanCBrammer]

We're providing PDF documentation that's build from Markdown and DOCX files.
Currently, we're building it manually.
It could be build automatically as part of the release workflow, using pandoc.

Make sure links work in PDF (currently, links referring to other markdown files within the repo are broken).

[nbehrnd]

@JanCBrammer Given pandoc showcases examples of its use as a GitHub Action (example), this approach may indeed help to keep the content across the different output formats (.docx, .html, .pdf) in sync.

Frequently, I check .md files for syntax consistency with markdownlint. Similar to pylint for Python, the utility indicates the lines where a revision can improve the file altogether with a hint how to improve it. It isn't an active code reformatter (like black, or ruff) and thus some sed is necessary to incorporate the suggestions.

[JanCBrammer]

Thanks for the pointers @nbehrnd! Linting the docs seems super useful.