Throttle connectivity check on connectivity issue

If Supervisor detects a connectivity issue, currenlty every function
which requires internet get delayed by 10s due to the connectivity
check. This especially slows down initial startup when there are
connectivity issues. It is unlikely to resolve immeaditly, so throttle
the connectivity check to check every 30s.

supervisor/supervisor.py

@@ -41,7 +41,7 @@ def _check_connectivity_throttle_period(coresys: CoreSys, *_) -> timedelta:
     if coresys.supervisor.connectivity:
         return timedelta(minutes=10)
 
-    return timedelta()
+    return timedelta(seconds=30)
 
 
 class Supervisor(CoreSysAttributes):