Support resumable user & document uploads

[eljhkrr]

Is your feature request related to a problem? Please describe.
It's frustrating when uploading a large batch of documents or creating many users and the process is interrupted for some reason, it has to start from the very beginning. With national scale deployments becoming common, large self-host partners are likely to encounter this challenge.

Describe the solution you'd like
Upload process should be able to intelligently resume from the interruption

Describe alternatives you've considered
The alternative is to manually review the upload report and delete uploaded documents/users from the batch and restart. This is very error prone.