don't notify if notification state pending

If notification state is pending and last update of state was made
less than a minute ago. In the case of a grafana instance is shut down/crashes
between setting pending state and before sending the notification/marks as complete
this logic should allow the notification to be sent after some time instead of
being left in an inconsistent state where no notifications are being sent.

pkg/models/alert_notifications.go

@@ -93,6 +93,7 @@ type AlertNotificationState struct {
 	SentAt     int64
 	State      AlertNotificationStateType
 	Version    int64
+	UpdatedAt  int64
 }
 
 type SetAlertNotificationStateToPendingCommand struct {
@@ -110,4 +111,3 @@ type GetNotificationStateQuery struct {
 
 	Result *AlertNotificationState
 }
-