Make "split value by delimiter" feature work together with reference data mapping

This would allow you to provide

org_types
a,b,c

and get a FOLIO array with three mapped reference data UUIDs.

It will require either extending mapper_base.get_mapped_value so it iterates over subdelimited values, or iterating over subdelimited values int he organizations_mapper and then adding a custom version of mapper_base.get_mapped_value which takes the value to be translated as ref data as an argument rather than the entire object.

Not sure if we will be seeing ref data arrays beyond organizations. Maybe for note types or statistical codes?

Start by reading mapper_base.get_mapped_value and organizations_mapper, the two entry points named in the issue. Determine how split values are represented and how reference data mapping currently handles an organization object. Done means a delimited value such as a,b,c produces an array containing the three mapped reference-data UUIDs, with the scope for other reference-data arrays clarified.

Written by the indexing model from the issue text.