Alerting: Support Unified Alerting with Grafana HA (#37920) (#39342)

* Alerting: Support Unified Alerting in Grafana's HA mode.

(cherry picked from commit 7db97097c9)

Co-authored-by: gotjosh <josue@grafana.com>

pkg/tests/api/alerting/api_admin_configuration_test.go

@@ -21,9 +21,9 @@ import (
 
 func TestAdminConfiguration_SendingToExternalAlertmanagers(t *testing.T) {
 	dir, path := testinfra.CreateGrafDir(t, testinfra.GrafanaOpts{
-		EnableFeatureToggles:              []string{"ngalert"},
-		DisableAnonymous:                  true,
-		NGAlertAdminConfigIntervalSeconds: 2,
+		EnableFeatureToggles:           []string{"ngalert"},
+		DisableAnonymous:               true,
+		NGAlertAdminConfigPollInterval: 2 * time.Second,
 	})
 
 	grafanaListedAddr, s := testinfra.StartGrafana(t, dir, path)