Client porcelain for copying packages between suites

The package_publish workflow provides a mechanism for copying packages between suite collections. However, in practice we also need a reasonable user interface for this.

From experience in Ubuntu, while a web UI is nice to have, it's more important to have a command-line client since this is the sort of thing you often want to be able to use in a programmable way (compare copy-package). I'd like to have something like debusine package copy (not debusine artifact copy, because this workflow is specific to packages in suites). This should also take command-line parameters in a way that's simpler than needing to write full lookups by hand.

This should also include the possibility to remove the package from the source suite (i.e. move rather than copy), which would require an addition to the package_publish workflow.

An obstacle to this is the rather generic/building-block nature of workflows: a given workspace may not have a template for the package_publish workflow, or the client may not know its name. I think we should solve this by providing a more opinionated workflow to create workspaces intended to host package repositories, which could set up the necessary workflows using well-known names.