Since today: Improved feedback when offer is blocked for policy reasons on product level

The new error code '3001' is introduced for the following endpoints: 'Get offer by offer-id' and 'Request unpublished offer report'. Earlier in such cases, a '4004' would be given with the message that 'You are the first to sell this product'. With the new error code, we try to provide more accurate feedback about the status of your offers.