Show notification when connectivity is limited
Plasma-nm already shows a little triangle in the tray when that happens but it can easily be missed. Show a notification when connectivity becomes limited.
There's a 10 second grace period before showing the notification as NM appears to briefly mark any connection as limited when connecting to it.
Used python http to simulate different responses for the connectivity check.
- Did not run the server: got a triangle and a notification after 10 seconds
- Ran the server with different response: got a captive portal notification right away as before
- Ran the server with correct response: got nothing, full connectivity
- Ran the server with different response, then shut it down: got a captive portal notification, it went away, and then 10 seconds later I got the limited connectivity notification
- Did not run the server, then ran it with different response: got a limited connectivity notification after 10 seconds, then had it replaced by a captive portal notification
Not sure 10 seconds are actually needed, when using the local python server it would directly go from disconnected to full but with networkcheck.kde.org it would briefly go to limited when I connect my wifi.
I'm open to suggestions on wording. Icon MR for breeze is frameworks/breeze-icons!44 (merged)