Add Feature Flag for Hearing Aid Profile

Using the Settings App-Developer Options-Feature Flag, allow the user to
enable or disable the Hearing Aid Profile.

Bug: 116317072
Bug: 116044083
Test: Manual testing using Settings App
Change-Id: I6716ac2e537570b9d3caadd5b622005312e0684e
Merged-In: I6716ac2e537570b9d3caadd5b622005312e0684e
(cherry picked from commit ab57e8a6)