Improve handling for DK ledger and tax codes per WooCommerce tax category

[aldavigdis]

Each tax code set in WooCommerce needs to support ledger codes and tax codes when creating a new product. DK tends to assume things when those are not specified, so we need to be able to set this manually.

Currently, there is limited support for ledger codes that needs to be expanded on.

This is how those look in the DK product UI:

[aldavigdis]

This seems to be solvable on the DK side by adding a ledger code for the purchasing side, which lets DK figure out the ledger codes for the product more effectively.

Being able to set this manually on our end may make things more flexible, so I'm getting this back to priority 3 instead of closing the ticket.