Issue:
With the "Extra Step During Checkout" setting,
it is possible to click on the "Configure Form" button
which should redirect us to the form in order to edit it.
However, we will always be redirected to the first website
(even if we have modified it in the settings).
Furthermore, if we don't have a cart in progress,
we will be redirected to the shop.

Solution:
Add a parameter specifying that it is for editing.
In this way, we can modify the form without having to create a cart.
Due to a technical limitation (reloading settings after saving),
we will always be redirected to the first website.
But it is possible to change the website (with the website editor)
and modify the second website if necessary.

opw-3245772

closes odoo/odoo#116975

Signed-off-by: Antoine Vandevenne (anv) <anv@odoo.com>