Use toggle type for active feature control.

[JakePT]

Description of the Change

Tweaks the settings schema to use toggle type for the enabled/disabled control.

Also makes some corrections/changes to the settings schema of some features:

• Use label instead of default for the content of markup controls.
• Use disabled instead of readonly for read-only controls (it turns out this works better).
• Use actual facets as options for the Filters control in Instant Results (with a correct default).
• Proper default for Instant Results search behaviour.
• Use a string value for Did You Mean search behaviour.
• Removed settings from Search feature that didn't belong there.

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.