Update CreateItemEventHandler to support a list of Items in event payload context after the mapping (MappingManager.map() will map multiple Items from single MARC Bib) - send separate requests to mod-inventory-storage to create each (or batch?)

CreateItemEventHandler.processMappingResult() calls fillHoldingsRecordIdIfNecessary() - make changes to associate each Item with a corresponding Holdings. DataImportEventPayload should contain a list of Holdings values (added in scope of ) to be used for associating Items with Holdings.

Event that Items are created should be published once and contain a list of successfully created entities and a list of errors if some failed to be created. 

Add tests