Add FolderUID for library elements (#79572)

* Add FolderUID in missing places for libraryelements

* Add migration for FolderUID in library elements table

* Add Folder UIDs tolibrary panels

* Adjust dashboard import with folder uid

* Fix lint

* Rename back FolderUID to UID

* Remove default

* Check if folderUID is nil

* Add unique indes on org_id,folder_uid,name and kind

* Update pkg/services/libraryelements/database.go

Co-authored-by: Sofia Papagiannaki <1632407+papagian@users.noreply.github.com>

* Fix folder integration test, with unique index on library elements

* Make folder uids nullable and rewrite migration query

* Use dashboard uid instead of folder_uid

* Adjust test

---------

Co-authored-by: Sofia Papagiannaki <1632407+papagian@users.noreply.github.com>

pkg/services/libraryelements/database.go

@@ -149,14 +149,20 @@ func (l *LibraryElementService) createLibraryElement(c context.Context, signedIn
 	}
 
 	metrics.MFolderIDsServiceCount.WithLabelValues(metrics.LibraryElements).Inc()
+	// folderUID *string will be changed to string
+	var folderUID string
+	if cmd.FolderUID != nil {
+		folderUID = *cmd.FolderUID
+	}
 	element := model.LibraryElement{
-		OrgID:    signedInUser.GetOrgID(),
-		FolderID: cmd.FolderID, // nolint:staticcheck
-		UID:      createUID,
-		Name:     cmd.Name,
-		Model:    updatedModel,
-		Version:  1,
-		Kind:     cmd.Kind,
+		OrgID:     signedInUser.GetOrgID(),
+		FolderID:  cmd.FolderID, // nolint:staticcheck
+		FolderUID: folderUID,
+		UID:       createUID,
+		Name:      cmd.Name,
+		Model:     updatedModel,
+		Version:   1,
+		Kind:      cmd.Kind,
 
 		Created: time.Now(),
 		Updated: time.Now(),