[IMP] point_of_sale: Show customer only and increase customer ranking.

Following the removing of the vendor and customer field, when we wanted to display customer in the back end, we saw all. We added a default filter when clicking on the menu button that displays only customer with a customer rank higher than 0.
We also increase their customer ranks everytime they make an order in the front end.

closes odoo/odoo#41769

Task-id: 2092483
Signed-off-by: pimodoo <pimodoo@users.noreply.github.com>