Support for using a different IDrive

[jtpio]

Currently Notebook 7 shows the default file browser on the /tree page:

However in JupyterLab it's also possible to use different drives to manage contents from other sources. For example:

• https://github.com/jupyterlab/jupyterlab-github
• https://github.com/jupyterlab-contrib/jupyterlab-filesystem-access

Ideally there should be a way to switch the default file browser in Notebook 7 to use a different drive.

Or add the drives to the tab panel:

[jtpio]

This might also be relevant: jupyterlab/jupyterlab#13512

[jtpio]

Technically drives seem to already be added to the left area automatically, and files and notebooks can be opened from the drive (at least with some drives):

notebook-7-drives.webm

Maybe they should still be placed in the tab panel as mentioned above.