Bluetooth MaxConnectedAudioDevices show correct number

* When the preference is changed by the user, it will update the UI
* When the Developer options is enabled, it will set the system property
to default number
* Change string "Maximum number of connected Bluetooth audio devices" to
"Maximum connected Bluetooth audio devices" per discussion with Lindsay

Bug: 71603731
Test: m
ROBOTEST_FILTER="BluetoothMaxConnectedAudioDevicesPreferenceControllerTest"
RunSettingsRoboTests -j40
Change-Id: I3e59534585065c84530da73ffded21894c845ce9