folderSize
Utility method as extension to OmhStorageClient to calculate the total file size of specified folder recursively.
Loops through entries of the files and folders at specified folder, and accumulate the file sizes. If encounter a folder, accumulates the total file sizes of the folder by calling folderSize().
Return
total file size of the specified folder
Parameters
folderId
folder ID. Refer to corresponding provider documentation for the value supported