If there are no default taxes on product or account, or
predictive guess, there should be no default taxes on a new aml.
So the `account_sale_tax_id` (and `account_purchase_tax_id`)
field only concern new products (as specified in the tooltip
of the field).
In Argentina, there is a constraint so all lines should have
a tax. So, we need to add default tax on their demo products.
We also add it to the products in account demo to have taxes
by default on demo invoices for all localizations.
task-3045026
Part-of: odoo/odoo#115222
gawa-odoo
15b2c690e1