feat(alerting): add feature toggles for alerting functions

pkg/services/sqlstore/migrations/alert_mig.go

@@ -1,8 +1,15 @@
 package migrations
 
-import . "github.com/grafana/grafana/pkg/services/sqlstore/migrator"
+import (
+	. "github.com/grafana/grafana/pkg/services/sqlstore/migrator"
+	"github.com/grafana/grafana/pkg/setting"
+)
 
 func addAlertMigrations(mg *Migrator) {
+	if !setting.AlertingEnabled {
+		return
+	}
+
 	alertV1 := Table{
 		Name: "alert_rule",
 		Columns: []*Column{