complete dump + restore via API

I'd like to be able to collect all the datasets, orgs, groups and users from a ckan instance and load them again via the API if I have admin access on both instances.

I can almost do this with `ckanapi dump` and `ckanapi load`, but users (including sensitive information like their emails and hashed passwords) and file contents in the filestore aren't yet supported.

Are there any limitations in the API that would prevent me from doing this?

@amercader like the harvester, this is another potential use for the "admins can set uuids via the API by default" dataset schema change that we talked about.

Start by reviewing the ckanapi dump and ckanapi load entry points, then inspect the API capabilities for users and filestore contents. Define the supported scope and validation for a complete admin-to-admin round trip; the issue names no files or tests, so substantial repository exploration is required.

Written by the indexing model from the issue text.