Alerting: Fix incorrect embedded DTO being returned when handling rule groups (#53701)

* Fix DTO embedding when getting/putting alert rule groups

* Drop usage of word 'Domain'

* Rename var as well

pkg/services/ngalert/models/alert_rule.go

@@ -113,6 +113,15 @@ var (
 	}
 )
 
+// AlertRuleGroup is the base model for a rule group in unified alerting.
+type AlertRuleGroup struct {
+	Title      string
+	FolderUID  string
+	Interval   int64
+	Provenance Provenance
+	Rules      []AlertRule
+}
+
 // AlertRule is the model for alert rules in unified alerting.
 type AlertRule struct {
 	ID              int64 `xorm:"pk autoincr 'id'"`