[hearing devices page][Audio routing] Add feature flag to control visibility...

[hearing devices page][Audio routing] Add feature flag to control visibility of the hearing device controls and audio output

* Setup basic xml for hearing device controls and audio output in bluetooth detail device page.
* Use same PreferenceCategory with spatial audio and rename to
  `feature_controls_group`

Bug: 237625815
Test: make RunSettingsRoboTests ROBOTEST_FILTER=BluetoothDetailsHearingDeviceControlsControllerTest
Test: make RunSettingsRoboTests ROBOTEST_FILTER=BluetoothDetailsAudioRoutingControllerTest
Change-Id: Ibe71757b53b9d65c6ab6efa1053d035e78882b68