ci/docs: updates related to building and testing documentation

[consideRatio]

This PR is about the documentation: improving developer experience, build and test automation, and fixes misc broken links etc.

• make linkcheck and make devenv is now available.
  • linkcheck checks for broken links
  • devenv starts a browser to view the built documentation, and rebuilds and refreshes the browser when documentation changes
• A github workflow job is added to run make linkcheck
• The github workflow building documentation is now stricter, failing on warnings. Note that we had a warning where we didn't have sqlalchemy as a dependency, which made the autodoc-traits fail to provide a configuration reference when inspecting all the .py files.
• Fixes various broken links and updates link that were redirecting, as found by linkcheck