Enable sink absolute volume based on flag

Problem: AAOS has disabled fixed volume flag. However, for cars
we still want to set the absolute volume.

Solution: Use automotive context to enable absolute volume.
If flag is enabled, then device will ignore the incoming volume
from phones. It will still continue to rely on audio manager's fixed
volume for other devices.

Bug: 312535397
FLAG_EXEMPT: Additional check and has test coverage.
Test: atest GoogleBluetoothInstrumentationTests:com.android.bluetooth
        .avrcpcontroller.AvrcpControllerStateMachineTest

Change-Id: I7a3685c64e6ada7bbe90e04baa17e3086ce0c40a