Install and enable Pipewire by default for non-audio related tasks

Related to https://gitlab.com/groups/postmarketOS/-/milestones/15#tab-issues and specifically #1827: Pipewire (+Wireplumber) are increasingly needed for camera and screen sharing/recording tasks. They should work well even is Pulseaudio handles audio - by simply not install pipewire-pulse etc.

Already having the service installed and running might also make switching the audio stack easier later on.