Build docs better in CI/CD

[CasperWA]

This change does away with the outdated and non-maintained GitHub action ammaraskar/sphinx-action. It is using an old version of the underlying Docker image sphinxdoc/sphinx (see also this source), which enforced everything running in Python 3.8 and not the actual Python version specified in the workflow here (Python 3.10).

The new way of building the documentation has been tested locally, and the CI here also seems to work as intended, so it should be good 👍
Instead of using the GH Actions, it simply utilizes the Makefile that exists in the sphinx folder. So we still install pandoc using APT and then from within the working directory sphinx we run make html, which will generate the documentation under sphinx/_build/html, which is the same as was done previously, i.e., the upload step does not need to change.

Finally, I've updated the versions of all dependencies where possible - testing everything locally.
The only package I've kept at the current version in pydata-sphinx-theme, as updating this to the latest version (v0.15.2 as of writing) resulted in a severe change in the look and feel of the documentation. Extra time, effort, and care should be taken when updating this package version at a later stage.

Note, also packaging has not been updated to v24 due to a version incompatibility with the latest version of EMMOntoPy.
Edit: Already done by @dependabot now.

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To see the built documentation do either of the following:

Unpack and view the built artifact:

• Go to the latest run of the build documentation workflow for this branch and download the documentationHTML artifact at the bottom of the "Summary" page (as of writing, this is the link to the artifact).
• This will download a zip-file to your system.
• Unpack it and find and open the index.html file.

Build the documentation locally and check it out:

• git clone this repository locally, preferably when running a virtual environment (see e.g., some documentation on venv and virtualenv).
• git checkout the branch cwa/fix-docs-building.
• From the current directory of the (possibly freshly cloned) repository, run the following commands in your shell/terminal:

  python -m pip install -U pip
  pip install -U pip setuptools wheel
  pip install -r requirements_docs.txt -r sphinx/requirements.txt

• Note, you need pandoc installed on you system. If you are running on Linux (natively or through WSL) this is as simple as installing it from your package manager of choice. E.g., using APT:

  sudo apt-get update && sudo apt-get install -y pandoc

  For more information about installing pandoc, see their documentation.
• Finally, if there have been no issues so far, you should be able to run the following commands to build the documentation as intended:

  python sphinx/ttl_to_rst.py
  cd sphinx
  make html

• Go to the sphinx/_build/html folder and open the index.html file in your browser of choice.

[jsimonclark]

@xavierr , could you please have a look at this and see what you think? If it's a good idea, we should consider updating our other CI/CD workflows with sphinx.

[CasperWA]

Updated this further to remove all Sphinx build warnings. In this way, the -W flag can also be added to the CI workflow, which will treat all warnings as errors, meaning if warnings are emitted in the future due to some changes, it will make the CI workflow fail. This is intended to ensure warnings are considered seriously by any contributor, making them consider whether the warning is something they should react on or is something that can be ignored (in which case it should manually be ignored from the configuration).

Note, to temporarily avoid having the documentation build fail on warnings (which are in their essence not critical), the -W flag can be removed from the SPHINXOPTS environment variable (see the relevant CI workflow):