Add support for custom progress callbacks for RDSS3 storage

So far, custom progress callbacks were only possible for non-RDSS3 resources. This PR adds support also for RDSS3 resources.

Furthermore, duplicated code in FileObject.update was removed and the wrapper function progress_callback is now defined inside the respective _upload_blob function to account for particularities of the uploading library.

mentioned in commit 4a653091

merged