Track webcam and microphone usage

https://github.com/antonfisher/go-media-devices-state

I think `webcam` and `microphone` could be two interesting additions to the heartbeat payload here. The idea would be:

If AFK is true but webcam and/or microphone are on, still treat this time as active. In other words, still track long-running video conferences as active time on the computer.

What do you think? Is this watcher the right place for it?