[FIX] account_edi_ubl_cii: handle paid invoice at import

The edi attachment (for every format in `account_edi_ubl_cii`) contains
a tag indicating whether the invoice is fully/partially paid.

Before this fix, when this tag was filled, a down payment section was
created on the invoice. For a fully paid invoice, the resulting amount
was then 0, so the invoice was marked as "Paid".

This was wrong. The correct amounts need to be kept on the invoices.
This fix no longer creates a down payment, instead a message is logged
in the chatter.

task-3264843
opw-3248200

closes odoo/odoo#120353

X-original-commit: 47905d21
Signed-off-by: Laurent Smet <las@odoo.com>
Signed-off-by: Julien Van Roy <juvr@odoo.com>