Migrate to JupyterBook 2

[MathewBiddle]

https://jupyterbook.org/

Or not...

[ocefpaf]

I experimented with this in the past and I have a branch I can push with it. The main issue I found was our gallery page. It uses a custom sphinx directive to render and I could not make it work with JB 2.

xref.: https://jupyterbook.org/stable/resources/upgrade/