Add LE Audio feature switcher in the developer option menu

Add a switcher to enable/disable LE audio feature. The switcher could be
enabled by setprop ro.bluetooth.leaudio_offload.supported=true

screenshot: https://screenshot.googleplex.com/6aGP664S9PX5EMS

Bug: 233018305
Bug: 233005340
Test: make RunSettingsRoboTests ROBOTEST_FILTER=BluetoothLeAudioPreferenceControllerTest
Test: switch LE audio feature, and check LE audio functionality status
Change-Id: I8adcf27edd1438df445d32fca93f35ff5020a3b3