Add optional retry for data upload operations

[guysmoilov]

They have a tendency to get interrupted, and an optional retry mechanism would really improve the experience. This will require care, since if the upload has any opened files, they either have to be re-opened or else the retry aborted.

[guysmoilov]

Another option would be to introduce a multi-step process to upload files one at a time, with retries, and then finally commit them all at once.