[Toggle] add the feature flag toggles to the live demo as options in the menu

[laurenmrice]

Acceptance criteria

• Add the feature flag toggles to the live demo as options in the menu.

• Name them something like: "Default toggle (preview)" and "Small toggle (preview)"

• Having said that the Tile and Structured list live demo names in the menu need to be updated from (unstable) to (preview) as well.