Allow users to change settings from a notebook view

[psychemedia]

Currently the Table of Contents sidebar seems to be collapsed by default and must be opened either from View > Table of contents or shift-command-k`.

It would be useful the show / hide setting could be set by default via a settings file.

Ideally, the user should also be able to change the default, but I note that the notebook UI does not seem to expose the Settings > Settings Editor option that JupyterLab provides?

[psychemedia]

Relates to: #6990

[jtpio]

Ideally, the user should also be able to change the default, but I note that the notebook UI does not seem to expose the Settings > Settings Editor option that JupyterLab provides?

It does, but only on the file browser page (/tree).

[RRosio]

Per triage: accepting this issue and re-naming it to reflect follow-up comments