During OPDS import, handle a collection link as an indicator that the work should be added to a CustomList

[leonardr]

A distributor that offers an OPDS or ODL feed should be able to convey ad-hoc collections of works that, on the circulation manager site, correspond to the work's membership in custom lists.

In a Slack discussion with Amy Slagle and Michael Atwood, we decided the simplest way to do this was through a link with rel="collection", the same link used by the circulation manager to present grouped feeds to an end-user OPDS client.

On the circulation manager side, this would mean configuring an OPDS or ODL import to pick up collection links and automatically add works to all corresponding custom lists based on the link's href or title, creating the custom lists if necessary.

[leonardr]

Duplicate of NYPL-Simplified/server_core#856. Closing this one because I do think the basic implementation needs to go into core.