Push datasets to remote CKAN

Whilst harvesting from other CKAN instances works, it doesn't give very much control to the owner of the harvested organisation in the local CKAN instance.

I would like to be able to push a single dataset, or a selection of datasets to a remote CKAN instance that is pre-configured. This might be a button on the dataset page (for publishing admins) or a bulk-update like form (currently under organization admin).

The remote CKAN instance might already be pre-configured and will obviously require an APIKey for the remote server. Datasets that are pushed should record the details of the remote URL (probably as some sort of extra as PackageRelationships only work for local packages).

The issue names no files or tests; start by reviewing the existing harvesting flow, the dataset page, and the organization-admin bulk-update entry point. Clarify the publishing-admin workflow, remote CKAN configuration and API-key handling, and how pushed datasets record their remote URL. Done should cover single and selected-dataset pushes with persisted remote details.

Written by the indexing model from the issue text.