Customize the shell layout with the settings

[jtpio]

Fixes #6688
Fixes #6386
Fixes #6915

• Add schema to define a user layout
• Add type to the shell.add() calls if any
• Add defaults?
• Add documentation, using the Voila Preview and the Markdown Preview as examples
• Add UI test
• Add the api-change GitHub label because the Shell namespace was renamed to INotebookShell

For now the page needs to be refreshed for the user layout to be effective.

layout-settings.mp4

[github-actions]

👈 Launch a Binder on branch jtpio/notebook/layout-settings

[andrii-i]

Core customization functionality looks and works well.

[jtpio]

Configuring the Voila preview with the following settings to open in the right area:

{
    "layout": {
      "Voila-preview": {"area": "right"}
    }
}

voila-preview.mp4

[jtpio]

This will also be useful to get the markdown preview, that we can add to the settings by default:

layout-settings-markdown.mp4

[jtpio]

bot please update playwright snapshots

[jtpio]

As discussed today at Notebook meeting, I opened an issue in JupyterLab to consider making the shell layout customization more generic between JupyterLab and Notebook 7: jupyterlab/jupyterlab#14685

It's not clear whether this can be addressed before the Notebook 7 final release, or if this should be considered for a future version.

So marking this as ready, although happy to make further improvements to the docs in follow-up PRs.

[andrii-i]

Customization works well. Tests and documentation look good as well. Thank you @jtpio.

[jtpio]

Thanks @andrii-i for the review!