Jupytext notebook support

[choldgraf]

Currently, we only support text-based notebooks via the {code-cell} directive and {eval} role. Jupyter Book v1 supports any file format that Jupytext supports, which is a wide variety of text-based notebook formats.

I don't see any mention of Jupytext support in the docs, so assume that it isn't supported right now.

Suggestion

We should either:

• Support Jupytext formats as a general principle for notebook execution and reading.
• Define the few jupytext formats that are most common and support them
• Explicitly agree to drop jupytext support in v2.

[agoose77]

This is a great issue Chris, thanks!

[parmentelat]

this issue resonates particularly strongly with me as I only write jupytext notebooks, given how git-unfriendly the ipynb format can turn out to be :)

hence I'd clearly advocate option 1 / full support as far as possible; this being said fyi, md:myst and py:percent would already account for a substantial coverage of my current courseware, the remaining being javascript and bash; but that's just me I guess :)

one other thing that has been discussed in other places was, it could be nice to be able to define a naming scheme that can tell notebooks from regular documents in my case for example, over time I have gone for *-nb.py or similar (which is helpful for humans too:), it would be nice to be able to configure just that when initializing the book; maybe something like

jupytext_patterns:
  - *-nb.py
  - *-nb.md

somewhere in myst.yml