[IMP] point_of_sale, pos_*: Enable HTTPS in POS

HTTPS had been disabled on SaaS to allow the use of the IoT Box that
had no valid SSL certificate. As of V13.0, IoT Boxes connected to
Enterprise DBs have a valid certificate. POS can then use HTTPS.

Nginx is configured to redirect all requests to `/pos/web` to HTTP,
so we change the POS URL to `/pos/ui`, except when using a Six
payment terminal as it only works in HTTP.

closes odoo/odoo#51625

Taskid: 2191878
Signed-off-by: pimodoo <pimodoo@users.noreply.github.com>