Load all settings from federated extensions at startup

[jtpio]

References

JupyterLab 4 seems to now be expecting all settings (including the ones from federated extensions) to be returned in one go on the first call to /api/settings.

This is likely related to the change in jupyterlab/jupyterlab#14195 and/or other upstream PRs as well.

Fixes #1213

Code changes

• Aggregate settings from federated extensions in a all_federated.json file by adding a step in the federated_extensions addon post_build
• UI test to check the "Launch Notebook File Browser" item is available when the notebook package is installed in the build environment
• Handle redirects to /doc/tree
• UI test to check going from Notebook to Lab with the toolbar button
• Mention installing the notebook package in the docs to get the UI elements

An alternative could have been to create an all.json file with all the settings for a federated extension, in each federated extension directory. And query this file for each extension. However many extensions don't provide settings, so these queries would lead to many 404s.

User-facing changes

End users should be able to see menu entries or toolbar items defined in third-party extensions via the settings system.

notebook-lab-switch.mp4

Backwards-incompatible changes

None

[github-actions]

👈 Try it on ReadTheDocs

[jtpio]

Thanks @bollwyvl for the review, I pushed a couple more commits to address the suggestions 👍

[jtpio]

Getting this one in and following up with a new release.