Add MFolderIDsServiceCount to count folderIDs in services pkg (#81237)

pkg/services/ngalert/tests/fakes/rules.go

@@ -9,6 +9,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/grafana/grafana/pkg/infra/metrics"
 	"github.com/grafana/grafana/pkg/services/auth/identity"
 	"github.com/grafana/grafana/pkg/services/folder"
 	"github.com/grafana/grafana/pkg/services/ngalert/models"
@@ -67,6 +68,7 @@ mainloop:
 			}
 		}
 		if existing == nil {
+			metrics.MFolderIDsServiceCount.WithLabelValues(metrics.NGAlerts).Inc()
 			folders = append(folders, &folder.Folder{
 				ID:    rand.Int63(), // nolint:staticcheck
 				UID:   r.NamespaceUID,