[FIX] website: prevent website duplicate from form view

At the moment, duplicating a website is not possible in the sense of
duplicating content, pages, etc. It is still available as an action from
the form view, and it could make sense to start up a new website with a
few common values (social media? etc?)... but many of website fields are
technical fields that should not be copied and many are dubious to copy
and not even visible in the form view. Really, duplicating a website at
the moment is misleading. This commit disables the possibility from the
form view.

In the future, we want to focus on the ability to export / import a full
website, but that's not for now.

opw-3782830

closes odoo/odoo#160587

X-original-commit: 43971a22c56b197306060ac3be7903d36d2c4be9
Signed-off-by: Romain Derie (rde) <rde@odoo.com>
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

addons/website/views/website_views.xml

@@ -22,7 +22,7 @@
             <field name="name">website.form</field>
             <field name="model">website</field>
             <field name="arch" type="xml">
-                <form string="Website Settings">
+                <form string="Website Settings" duplicate="0">
                     <sheet>
                         <group name="domain">
                             <field name="name"/>