[FIX] sale_quotation_builder: land on website in backend when editing

The quotation templates got a button to design them, which lands on
their website/frontend preview.
The goal is to then be able to enter edit mode and customize it.
But since we merged frontend > backend with [1] (and multiple iterations
since then), landing on the frontend is not a good idea to do that as
you would then need to click on the "Editor" button to go back to the
backend and be able to enter edit mode. Now we reach the iframe preview
directly.

Note: this will be improved in a further update to not require a reload
of the backend when clicking on the button.

[1]: https://github.com/odoo/odoo/commit/31cc10b91dc7762e23b4bde9b945be0c4ce3fe3b

X-original-commit: a98ea96b52f6ccfd43e364720001ed4c4bcbcb4e
Part-of: odoo/odoo#102787

addons/sale_quotation_builder/models/sale_order_template.py

@@ -20,5 +20,5 @@ class SaleOrderTemplate(models.Model):
         return {
             'type': 'ir.actions.act_url',
             'target': 'self',
-            'url': '/sale_quotation_builder/template/%d' % self.id
+            'url': '/@/sale_quotation_builder/template/%d' % self.id
         }