Add footer to app usage page

 - Add a footer to present the description text, will present specific text once this app is optimized or unrestricted only
 Screenshots:
   https://screenshot.googleplex.com/4HZGQU6SDni3PdR.png
   https://screenshot.googleplex.com/9gLSgftmaYuZepf.png
   https://screenshot.googleplex.com/55masP3VoAtAFMo.png

Bug: 178197718
Test: make SettingsRoboTests
Change-Id: Iced0fa591faf72874e2e3dff942122c90d35a4e7