Run documentation notebooks on CI

[nilsvu]

To make sure that notebooks in docs/ keep working, we should run them on CI. They need Pybindings compiled, so we either compile those in the docs CI job, or run the notebooks in one of the unit test workflows. To have the updated output in the notebooks show up in the docs it would be easier to run them in the docs CI job.
Another consideration is sample data that the notebooks need. We either make sure they run fast and without any sample data, or we allow them to use external data in which case they would be harder to test.