[FIX] pos_discount: default product
[FIX] pos_discount: default product

Several issues:
- If product `product_product_consumable` was deleted, an error is
  raised.
- The default values are inconsistent with the fact that
  `module_pos_discount` is `False` at POS creation.
- The domain should ensures that both `available_in_pos` and `sale_ok`
  are `True`, otherwise the product won't be loaded by the POS.

opw-814426

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo