Customize layout from settings

[jtpio]

Support for customizing the layout via the settings was added in JupyterLab in jupyterlab/jupyterlab#11614.

It's available in the latest JupyterLab 4.0 pre-releases.

With it, end users should be able to configure where widgets should be placed in the application shell. For example to be able to open terminals in the right area instead of a new tab.

For now it seems to be tied to the @jupyterlab/application-extension:shell plugin, which is not loaded in Notebook 7.

[jtpio]

This might help with #6386.

[jtpio]

In its settings, JupyterLab makes it possible to define the layout for single and multiple (document): https://github.com/jupyterlab/jupyterlab/blob/e0b4de1eb37c9dd37c11e5319ed00cb8d37b8d92/packages/application-extension/schema/shell.json#L32-L42

"properties": {
  "single": {
    "$ref": "#/definitions/layout",
    "default": {
      "Linked Console": { "area": "down" },
      "Inspector": { "area": "down" },
      "Cloned Output": { "area": "down" }
    }
  },
  "multiple": { "$ref": "#/definitions/layout", "default": {} }
}

For Notebook 7, maybe it could be interesting to offer the ability to customize per page.