Alerting: Enable flag alertingApiServer by default (#98282)

* enable flag alertingApiServer by default
* remove feature flag toggle in integration tests
* disable flag for old API tests

pkg/tests/api/alerting/api_alertmanager_test.go

@@ -22,6 +22,7 @@ import (
 	"github.com/grafana/grafana/pkg/expr"
 	"github.com/grafana/grafana/pkg/infra/db"
 	"github.com/grafana/grafana/pkg/infra/tracing"
+	"github.com/grafana/grafana/pkg/services/featuremgmt"
 	apimodels "github.com/grafana/grafana/pkg/services/ngalert/api/tooling/definitions"
 	ngmodels "github.com/grafana/grafana/pkg/services/ngalert/models"
 	ngstore "github.com/grafana/grafana/pkg/services/ngalert/store"
@@ -49,6 +50,9 @@ func TestIntegrationAMConfigAccess(t *testing.T) {
 		EnableUnifiedAlerting: true,
 		DisableAnonymous:      true,
 		AppModeProduction:     true,
+		DisableFeatureToggles: []string{
+			featuremgmt.FlagAlertingApiServer,
+		},
 	})
 
 	grafanaListedAddr, env := testinfra.StartGrafanaEnv(t, dir, path)