Video streams: provide live status information

[ES-Alexander]

Expanding on some suggestions in #800, we should support:

• [ ] an optional debug/quality overlay in the Video widget, showing FPS, bitrate, and dropped frames
• [ ] optional recording/logging of those values
  • relevant to #621 if logging to the subtitle files
  • even if it's just stored in Cockpit's logs and saved/accessed separately, that should still be much faster to check than scrubbing through a long video recording
    • if we do this approach then we should probably run an automated video quality check after each recording, and notify of potential problem periods and/or provide a graph of video health over time (which could potentially replace #800)
• [ ] a "video health" mini-widget, tied to an incoming video stream in the same way the recording widget is
  • I'm imagining a video symbol (per connected stream) in the top right mini-widget bar, with the symbol colour/icon based on thresholds for quality, e.g.
    • green video-camera --> all good
    • yellow video-camera --> some dropped frames, or inconsistent FPS/bitrate
    • yellow video-camera with black exclamation --> bad enough that investigation is recommended
    • red video-camera with black exclamation --> poor quality - footage unlikely to be usable
    • grey video-camera with red cross --> camera stream not detected as available
    • status changes could also create text notifications for the notification bar
  • hovering over the icon should show
    • status highlights (i.e. the cause of the status, like "low FPS, 21.3/25")
    • any corresponding recommendations (check power supply, camera temperature, etc), and
    • an obvious marker on any visible players of the video stream it's connected to (e.g. a red border on the widget(s), or fading/blurring all the other widgets)
  • clicking on the icon should either
    • open a pop-up showing the video quality info + common troubleshooting tips, or
    • toggle the debug overlay for any corresponding video widgets that are using that stream

[Williangalvani]

relevant code: https://github.com/selkies-project/selkies-gstreamer/blob/main/addons/gst-web/src/app.js#L387-L434