[FIX] website: delete page on cascade when deleting a website

The user is never able to delete a website, since there is at least one page,
the homepage, which is bootstraped during website creation.
From that point, even if nothing was done on that website, it was not possible
to remove it.
As website deletion is already a technical thing (debug mode), and since
website.page do not make sense without their website, removing those on cascade
will allow the user to remove a non-modified website.

task-2092845

closes odoo/odoo#44957

Signed-off-by: Romain Derie <rdeodoo@users.noreply.github.com>

addons/website/models/website_page.py

@@ -26,7 +26,7 @@ class Page(models.Model):
     header_color = fields.Char()
 
     # don't use mixin website_id but use website_id on ir.ui.view instead
-    website_id = fields.Many2one(related='view_id.website_id', store=True, readonly=False)
+    website_id = fields.Many2one(related='view_id.website_id', store=True, readonly=False, ondelete='cascade')
     arch = fields.Text(related='view_id.arch', readonly=False, depends_context=('website_id',))
 
     def _compute_homepage(self):