[FIX] l10n_fi : set confrorm payment ref on invoice

Steps :
Install eCommerce and l10n_fi.
Create a Payment Acquirer with a new Journal.
Change this Journal's type to Sales.
Go to Website, order a Product with this Acquirer.
Go to Sales > the consequent SO. Note the Payment Ref.
Confirm, Create Invoice and Post.
Note the same Payment Reference.

Issue :
This reference is not valid in Finland accounting because letters are
not allowed.

Cause :
First, a Journal linked to an Acquirer should be
of type Bank or Cash. Such Journals do not have Payment References
specifications. So, in the current state of affairs, it would not be
possible to set a localized reference on the SO.
Second, SO's payment reference is its name or CUST/its partner's id.
Then it is copied to its Invoice's payment reference.
Upon posting this invoice, if it has a reference, it is not modified.

Fix :
Limit the modification of the Type of a Journal linked to a
Payment Acquirer to : Bank and Cash.
Create a Finnish Sale module to compute SaleOrder.reference form itself
the same way AccountMove.invoice_payment_ref is computed from its name.

opw-2745902

closes odoo/odoo#87706

Signed-off-by: Onockx Audric (auon) <auon@odoo.com>