[TECHNICAL SUPPORT] LPS-42856 Asset Publisher does not export/import correctly document-subtype preference.

Hi Máté,

This PR is from @zsagia. He told me that you gave him guide lines about where and how to fix this issue. I found it OK in scope of source format and logic as well. Tested it also and seems to be fine.

Please review it and send it forward if you find it OK.

Regards,
Vilmos