Respects device policy to disble quick affordances

- Interactor updated to check DevicePolicyManager
- Documentation section added

Bug: 268218507
Test: Unit test added
Test: When hard-coded flag to disable all keyguard features, manually
verified that: (a) shortcuts don't show on lock screen, (b) wallpaper
picker does ot display "shortcuts" item, (c) settings app doesn't
display "shortcuts" item.

Change-Id: Ie21ad7e8213d63b6505a16a6a09d4675c7112b34