Alert when a camera stream is down

[mriamnobody]

We often don't know that the camera stream is down. A feature that alerts users through Telegram message or any other notification service that a camera stream is down will be a lifesaver for many other users of this tool and me.

[solderzzc]

Detector can't detect a camera disconnect event, it's a status change from home-assistant side, need figure out how to configure a event triggered by device status changes from home-assistant.