Changes to Get listing creation actions

the request property items/items/end_time became nullable

the request property items/items/start_time became nullable

the request property taker became nullable

the request property use_creator_fee became nullable

added the optional property code to the response with the 401 status

added the optional property code to the response with the 403 status

added the optional property code to the response with the 404 status

added the optional property code to the response with the 409 status