This is part of a profile.
Command on the other hand would look like this:
incus config device add <instance_name> PulseSocket1 proxy bind=instance listen=unix:/home/username/pulse-socket connect=unix:/run/username/1000/pulse/native security.uid=1000 security.gid=1000 uid=1000 gid=1000 mode=0777
You can see how I enable pipewire and pulseaudio inside containers here.