fix: delete folders using postorder (#113493)

* fix: delete folders using postorder

* chore: use helper function and do not add method to Folder store

- addresses other review comments fixing log messages and cleans up the unit tests

* chore: run library element tests on modes 2,3,5 only

* chore: adjust to folder.SortByPostorder(folders []*Folder)

* chore: run library panels tests in mode 2,3,5 only

* chore: run tests in all modes and increase timeout

- adjusting the modes and tweaking configs will be done separately

pkg/services/folder/folderimpl/folder_unifiedstorage_test.go

@@ -880,6 +880,7 @@ func TestIntegrationDeleteFoldersFromApiServer(t *testing.T) {
 		registry:               make(map[string]folder.RegistryService),
 		features:               featuremgmt.WithFeatures(),
 		tracer:                 tracer,
+		log:                    slog.New(logtest.NewNopHandler(t)),
 	}
 	user := &user.SignedInUser{OrgID: 1}
 	ctx := identity.WithRequester(context.Background(), user)