Run notebooks in CI

[huard]

The notebooks defined here are not actually run by sphinx, they're just rendered to HTML on ReadTheDocs. Testing actually occurs on Jenkins, which is not directly connected here. I think we could improve on our development cycle by having an action that runs the notebooks here for each PR.

Why this hasn't been done yet is because installing all the dependencies for the notebooks is really long and the resulting environment pretty big. Also, we don't want to test the environment itself, we want to test the notebooks.

One solution could be to write an action built on the same docker image used for the jupyterlab kernels.
https://docs.github.com/en/actions/creating-actions/creating-a-docker-container-action
The action would download the image, create a container, then simply execute pytest --nbval on the notebooks. If no errors are raised, this means the notebooks will run on the prod instance.

[Zeitsperre]

I've already created a new repository based on this idea (and a team for general workflow/DevOps-related work @Ouranosinc/devops). The new repo is at: https://github.com/Ouranosinc/jupyter-pavics-docker-action

It should be really simple to get something up and running. I'd like to see us write an action that can be configured to be useful for testing a few PAVICS-related components, if possible, but let's start with something that gets the job done here.

[Zeitsperre]

Relevant discussion concerning @huard's idea to upload prebuilt docs to ReadTheDocs: readthedocs/readthedocs.org#1083