Add Doxygen CI job and enforce Doxygen warnings

[ChrisThrasher]

Subject of the issue

Doxygen has some helpful warnings that we’re currently ignoring. We ought to elevator those warnings to errors then add a CI job to build the docs to prevent regressions. For example these warnings caught a docs bug for an sf::Context constructor that remained unnoticed for a year or more.

[ChrisThrasher]

Here is where I generate docs for the sake of catching warnings: https://github.com/ChrisThrasher/argon/blob/fa7b4b75d49eefb1cbeb7bc236dbdcc14e80e407/.github/workflows/ci.yml#L132-L147

Here is where I generate docs for the sake of deploying to GitHub Pages: https://github.com/ChrisThrasher/argon/blob/fa7b4b75d49eefb1cbeb7bc236dbdcc14e80e407/.github/workflows/cd.yml#L15-L44

In our case we don't care about GitHub pages per se but between these two jobs we should be able to figure out the best way to generate docs and create a release artifact from them so we can easily deploy them to the website.