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_configuration_test.go

@@ -17,6 +17,7 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
+	"github.com/grafana/grafana/pkg/services/featuremgmt"
 	apimodels "github.com/grafana/grafana/pkg/services/ngalert/api/tooling/definitions"
 	"github.com/grafana/grafana/pkg/services/org"
 	"github.com/grafana/grafana/pkg/services/org/orgimpl"
@@ -398,6 +399,7 @@ func TestIntegrationAlertmanagerConfigurationPersistSecrets(t *testing.T) {
 		EnableUnifiedAlerting: true,
 		DisableAnonymous:      true,
 		AppModeProduction:     true,
+		DisableFeatureToggles: []string{featuremgmt.FlagAlertingApiServer},
 	})
 
 	grafanaListedAddr, env := testinfra.StartGrafanaEnv(t, dir, path)