Create IIIF collections with PROCESSED child items

[tomcrane]

Update existing Create endpoint to support creating IIIF Collections

part 2:

create IIIF collection which has items

Acceptance Criteria:

TBC - Need to decide how items[] is processed on the way in and mutated on the way out for IIIF Collections.

[tomcrane]

At this point the child items are still external?
YES - defer internal item references for now