Configuration to declare additional cell-metadata keys to be considered as valid.

[nthiery]

In my course notebooks, I am using extensively tools such as nbgrader or rise/jupyterlab-deck which use custom cell-metadata (respectively nbgrader={...}, slideshow={...}). The myst CLI is (rightfully) not aware of these metadata; and complains:

⚠️  Devoirs/PremiersCalculs/01-valeurs-types.md:921 unexpected option "nbgrader" provided for directive: code-cell

This is producing hundreds of warnings which means the important warnings are not well visible.

Proposal

Add configuration to either silence completely myst CLI's complaints about unknown cell metadata, or better to register additional cell metadata keys that should be considered as valid. Something like:

project:
  ...
  additional-cell-metadata-keys: ['nbgrader', 'slideshow']

Thanks :-)