Pipewire: API to set identifying properties

It would be nice for users of the pipewire backend to have a way to set identifying properties on the stream, especially for ie. music players. This isn't a problem on Windows or MacOS since the APIs for metadata are separate from those for playback, but with pipewire you kinda have to be able to set them on the cpal-owned stream.

Maybe a new StreamExt trait similar to those in std ?