Extend Delete method so that a directory can also be deleted

[2S-Software]

Please extend the existing 'delete' method so that an empty directory can also be deleted. An exception is currently thrown because a file is expected as relativePath.

Perhaps add a new parameter 'isDirectory' like this:

 await icloudSyncPlugin.delete(
    containerId: containerId,
    relativePath: relativePath,
    isDirectory: true,
  );