Upgrade to latest pydata-sphinx-theme and myst-nb

[maximlt]

• Bumped the minimum pin of myst-nb, myst-parser, sphinx and pydata-sphinx-theme as this is what I tested. Let's see if our environments can solve with these pins.
• pydata-sphinx-theme updated (for performance reasons) their code that decides whether to include a toctree in the sidebar, which broke our approach. Instead, I used an approach (found it in the IPywidgets repo) that consists of adding a single sidebar template dedicated to the index page. It's configured in the shared conf.py file, nbsite users can easily override it.
• Had to update a Sphinx patch, I added a test to catch that regression.

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• [x] Section Navigation also needs to be removed from the non-index sidebars.
• [x] Migrated the front-end jQuery code to pure JS that switches between "backends" in a gallery, as the newer versions of the stack doc build stack no longer include jQuery.

[hoxbro]

I assume you are already aware, but just if you are not the myst-nb 1 gave problems for panel and holoviews documentation build: https://github.com/holoviz-dev/nbsite/pull/292

[maximlt]

I assume you are already aware, but just if you are not the myst-nb 1 gave problems for panel and holoviews documentation build: https://github.com/holoviz-dev/nbsite/pull/292

I'm an idiot I read geoviews somehow. Then I'll guess I'll build HoloViews and see how that goes.