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: 116725094
Bug: 116044083
Test: Manual testing using Settings App
Change-Id: I16b51d7feabc914219c24731eb39a23bd1782571
Merged-In: I16b51d7feabc914219c24731eb39a23bd1782571
(cherry picked from commit 068c2547)