ENH/MAINT: avoid overwriting the HtmlTranslator

[12rambau]

Fix #143, Fix #94

In this PR I tried to get rid of the custom BootstrapHTML5Translator. To remain compatible with what was built previously I simply edit the table nodes using a Sphinx post_transform.

here:
https://github.com/pydata/pydata-sphinx-theme/blob/main/src/pydata_sphinx_theme/bootstrap_html_translator.py#L24

We add an aria-level on a specific component of the output. In fact, what is done is a rough overwriting of this:
https://github.com/sphinx-doc/sphinx/blob/fa6d42597f2c1259ccdd9166763657bd9c2a316e/sphinx/writers/html5.py#L370
I don't manage to make it work with a post_transform so I think the solution is a directive overwrite. Before I loose some hair on this one, can someone explain why it's relevant for the theme ?

PS: this work is a WIP but I wanted to see the distant build to try to understand why there is this aria-level addition.
PPS: of course I will drop the second python file entirely when this will work

[choldgraf]

Maybe @jorisvandenbossche can provide context for why this translator exists? I believe he was the one to add it back in the day

[12rambau]

Superceeded by #1105