Navigation - Add feature toggle to settings

In order to allow users to enable or disable the new navigation, we add a new section under the Settings tab in the user's preferences. We can use this section to give some information about the new navigation to the user before they enable it.

This mockup does not match the description given here, as it shows the options under a new Features tab, but it serves to illustrate the point

Resources

Meta issue #32794 (closed) - Global and Contextual Navigation