[UR tweaks] Show the rich text toolbar and the minimap by default

[kacperpONS]

What is the context of this PR?

Following User Research we've identified the need to change the default behaviour of the Wagtail editor - we want the rich text toolbar to be pinned at the top of the input field and the editor minimap to be shown.

Functional tests have been added to check for the default behaviour and storing user preferences.

Walkthrough: https://www.loom.com/share/52fb408fa2d24b3290a2977b3ff919f2

How to review

1. Run Wagtail and open it in an incognito window (alternatively clear local storage in the dev browser console).
2. Go to page editor and check that:
   • the rich text toolbar is pinned at the top of the input field.
   • the page editor minimap is shown on the right
3. Then unpin the toolbar and hide the editor then refresh the page to check that the preference is saved.

Also, run the functional tests.

Link to Jira

https://jira.ons.gov.uk/browse/CMS-353

[MebinAbraham]

Can you add a screencast for this please.

[zerolab]

LGTM, with a minor (non-blocking) nitpick.

[sanjeevz3009]

Reviewed!