workspace: Play sound when an output is (un)plugged

As direct user feedback the the cable is working, even if the output itself is not configured or turned off.

Similar to how we play a sound when a USB stick is plugged in even if there's not any partitions with data you can mount.

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Plugged in HDMI, got a sound, unplugged it, got another sound.

Didn’t try any sophisticated changes, like plugging an entire external GPU in...