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/api/api_provisioning_test.go

@@ -515,7 +515,7 @@ func createInvalidAlertRuleGroup() definitions.AlertRuleGroup {
 	return definitions.AlertRuleGroup{
 		Title:    "invalid",
 		Interval: 10,
-		Rules:    []models.AlertRule{{}},
+		Rules:    []definitions.ProvisionedAlertRule{{}},
 	}
 }