AlertNotifications: Translate notifications IDs to UIDs in Rule builder (#19882)

* AlertNotifications: Translate notifications IDs to UIDs in alert Rule builder

* Avoid shadowing errors, raise validation error on non-existing notification id

* create a cache for notification Uids to minimize db overhead

* add cache usage test

* avoid caching empty notification Uids

* isolate db in alert notificationUid caching tests

pkg/services/sqlstore/sqlstore.go

@@ -99,6 +99,7 @@ func (ss *SqlStore) Init() error {
 
 	// Register handlers
 	ss.addUserQueryAndCommandHandlers()
+	ss.addAlertNotificationUidByIdHandler()
 
 	if ss.skipEnsureDefaultOrgAndUser {
 		return nil