Customer displays were all using the same URL and therefore could only
show the same products. We now use different URLs per screen.

Two screens connected to the same IoT Box can now display customer
displays from different POS.

closes odoo/odoo#41026

Taskid: 2123511
X-original-commit: 12569b0e
Signed-off-by: Antoine Prieëls <aprieels@users.noreply.github.com>