Adapt to xscen-509

[aulemahal]

Pull Request Checklist:

• pre-commit hooks are installed/active in my local clone ($ pre-commit install)
• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes attributes created by intake-esm contain illegal characters #13
• (If applicable) Documentation has been added / updated (for bug fixes / features)
• If a merge request has been made in parallel to this PR in xscen-notebooks, it is merged and the submodules have been updated. MR#6
• HISTORY.rst has been updated (with summary of main changes)
  • Link to issue (:issue:number) and pull request (:pull:number) has been added

What kind of change does this PR introduce?

• Use cat: to prefix dataset attributes generated from catalogs.
• New xscen.utils.get_cat_attrs that outputs a dictionary of those attributes without the prefix.

Does this PR introduce a breaking change?

Yes (but it comes from intake-esm)

Other information:

The intake-esm change also affects how lists are parsed :
https://github.com/intake/intake-esm/blob/ba4bb59ca1174369ff45a09aed030db0a7aa49d2/intake_esm/source.py#L100-L105

I.e.: every object that is iterable (like lists or tuples) is formatted as a comma-separated string. I think this doesn't break xscen, but might be worth noting. The only list-like attribute we usually use is variable.

[RondeauG]

Looks good!

[juliettelavoie]

ben beau

[aulemahal]

@Zeitsperre J'ai modifié l'action github pour exclure "docs/notebooks".