Generate HTML pages from docstrings
This MR introduces HTML doc generation from doscstrinngs using pdoc3. For our specific project it looks easier to integrate than sphinx. I previously considered pydoctor, but it does not work particularly well with our docstring formatting choices (it assumes docstrings are epytext).
HTML files will be generated under docs/build by a newly introduced make-html-docs CI job. Under the hood this calls a
make html-docs target that is available outside of CI too. This MR only takes care of generating the doc.
Publishing requires integrating the job with https://gitlab.wikimedia.org/repos/releng/docpub.
This MR bumps the base openjdk CI image to openjdk-11-jdk:11.0.18-s0-20230604 (Debian Bullseye), that ships with Python 3.9. A version bump of Python was required to address compat issues with pydoc
Bug: T336488
Bug: T337475