Use transfer --move on guest conversion

[wiswedel]

Converted guests (#208) shouldn't have to see the "transferred from..." folder as their only object after their conversion.
Instead, the conversion should use the new --move method (nextcloud/server#16439) to transfer the files.

• Requires Various fixes for transfer ownership server#16439

[wiswedel]

CC @ChristophWurst

[ChristophWurst]

This can be looked into once nextcloud/server#16439 has been integrated.

[rullzer]

Done