Propose COAR notify integration & endpoint schema for the API server

[ships]

This needs to be an extension to the API server proposal (#1). However it is out of scope for the initial RFC. From a comment on that proposal:

Following conversation with COAR Notify, this server should be designed so that Notify payloads include links to this server's resources. That means endpoint that retrieving the history for a given document, possibly including a query parameter that speaks to a specific event or point in time -- i.e. deal directly with the IRIs of actions/events links with link-relations should be included a la https://signposting.org/ and http://www.iana.org/assignments/link-relations/link-relations.xhtml

The basic idea here is that instead of wanting to update FROM a certain point in time, the COAR notification may inform an interested party that there exist new docmap objects at a certain location, and inform the interested party about the name (i.e., IRI) of one or more of the objects (let's say, Actions). This party does not know about the Timestamp of the action, nor does she know about a Cursor, but does know about the IRI. So they may want to initiate a sync as regards FROM that IRI's inclusion in the dataset.