fix: delete subfolder dangling panels (#113419)

* fix: delete subfolder dangling panels and error if used

* chore: add observation about library panel DeleteInFolders

- logs folders UIDs on DeleteInFolders error

* chore: add integration test for blocking library panel deletion and handling dangling library panels

* chore: fix integration test on mode 4 and 5

pkg/services/folder/folderimpl/folder_unifiedstorage.go

@@ -644,6 +644,21 @@ func (s *Service) deleteFromApiServer(ctx context.Context, cmd *folder.DeleteFol
 			return folder.ErrFolderNotEmpty.Errorf("folder contains %d alert rules", alertRulesInFolder)
 		}
 
+		libraryPanelSrv, ok := s.registry[entity.StandardKindLibraryPanel]
+		if !ok {
+			return folder.ErrInternal.Errorf("no library panel service found in registry")
+		}
+		//	/* TODO: after a decision regarding folder deletion permissions has been made
+		//	(https://github.com/grafana/grafana-enterprise/issues/5144),
+		//	remove the following call to DeleteInFolders
+		//	and remove "user" from the signature of DeleteInFolder in the folder RegistryService.
+		//	Context: https://github.com/grafana/grafana/pull/69149#discussion_r1235057903
+		//	*/
+		// Obs: DeleteInFolders only deletes dangling library panels (not linked to any dashboard) and throws errors if there are connections
+		if err := libraryPanelSrv.DeleteInFolders(ctx, cmd.OrgID, folders, cmd.SignedInUser); err != nil {
+			s.log.Error("failed to delete dangling library panels in folders", "error", err, "folders", strings.Join(folders, ","))
+			return err
+		}
 		// We need a list of dashboard uids inside the folder to delete related dashboards & public dashboards -
 		// we cannot use the dashboard service directly due to circular dependencies, so use the search client to get the dashboards
 		request := &resourcepb.ResourceSearchRequest{