bluez5: add Opus as a (Pipewire-specific) A2DP vendor codec
Support Opus as A2DP vendor codec.
The specification for vendor A2DP codec is our Pipewire-specific one, so it is compatible only with devices running Pipewire.
The main point here probably is that the codec supports passing multichannel audio over Bluetooth between devices running Pipewire, which cannot be done by other BT codecs.
Closes #2365 (closed)