feat: autocomplete MetadataType object when getting deposit datafiles list and specific datafile

• autocomplete MetadataType on deposit data list

    /dlcm-ingestion/preingest/deposits/{depositId}/data

• autocomplete MetadataType on deposit data item

    /dlcm-ingestion/preingest/deposits/{depositId}/data/{dataId}

• do not fill data without MetadataType with empty metadataType property

    "metadataType": {
       ...
    }

  but return

    "metadataType": null

  instead.