Alerting: Verify receiver permission read on rule create/update (#94286)

* Alerting: Verify receiver permission read on rule create/update

pkg/services/ngalert/models/notifications.go

@@ -35,6 +35,10 @@ type NotificationSettings struct {
 	MuteTimeIntervals []string        `json:"mute_time_intervals,omitempty"`
 }
 
+func (s *NotificationSettings) GetUID() string {
+	return NameToUid(s.Receiver)
+}
+
 // NormalizedGroupBy returns a consistent and ordered GroupBy.
 //   - If the GroupBy is empty, it returns nil so that the parent group can be inherited.
 //   - If the GroupBy contains the special label '...', it returns only '...'.