Extend Mapper.map() logic to check if the entity to be mapped is Holdings.

Get the Mapping rule for Holdings location from MappingDetails

Read list of values (Holdings locations) from the MARC record and store it in the DataImportEventPayload (list should contain all values including duplicates if there are such)

After Holdings entity is mapped (one json without the location) update DataImportEventPayload to contain the list of Holdings (as many as there are locations) - copy mapped Holdings, but set the location

Cover following cases with tests - single MARC field containing location (therefore one Holdings is mapped, but stored in the list nonetheless), multiple MARC fields containing location, but the location value is the same (single Holdings is mapped), multiple MARC fields containing location, values are different (multiple Holdings are written in the event payload)