Add an iso setting for disabling the document outline in the List View

Make it possible to disable the document outline in the list view by setting it to true or false in `applyDefaultSettings`.
Add a condition to `ListViewSidebar` that enables or disables the document outline based on this setting.

My use case: I use an isolated block editor to demo single blocks, and I want to hide the document outline to reduce noice.
I can do this locally in my own project, but it might benefit others too.

Locate applyDefaultSettings and ListViewSidebar, then trace how the list view currently decides whether to show the document outline. Add the boolean setting and verify that both true and false produce the expected outline visibility in the list view.

Written by the indexing model from the issue text.