Alerting: Support for simplified notification settings in rule API (#81011)

* Add notification settings to storage\domain and API models. Settings are a slice to workaround XORM mapping
* Support validation of notification settings when rules are updated

* Implement route generator for Alertmanager configuration. That fetches all notification settings.
* Update multi-tenant Alertmanager to run the generator before applying the configuration.

* Add notification settings labels to state calculation
* update the Multi-tenant Alertmanager to provide validation for notification settings

* update GET API so only admins can see auto-gen

pkg/services/ngalert/api/api.go

@@ -57,7 +57,7 @@ type API struct {
 	TransactionManager   provisioning.TransactionManager
 	ProvenanceStore      provisioning.ProvisioningStore
 	RuleStore            RuleStore
-	AlertingStore        AlertingStore
+	AlertingStore        store.AlertingStore
 	AdminConfigStore     store.AdminConfigurationStore
 	DataProxy            *datasourceproxy.DataSourceProxyService
 	MultiOrgAlertmanager *notifier.MultiOrgAlertmanager
@@ -115,6 +115,9 @@ func (api *API) RegisterAPIEndpoints(m *metrics.API) {
 			log:                logger,
 			cfg:                &api.Cfg.UnifiedAlerting,
 			authz:              ruleAuthzService,
+			amConfigStore:      api.AlertingStore,
+			amRefresher:        api.MultiOrgAlertmanager,
+			featureManager:     api.FeatureManager,
 		},
 	), m)
 	api.RegisterTestingApiEndpoints(NewTestingApi(