[PERF] mail: no memoryerror from slow load_message_failures

Earlier PR improved ACLs in Discuss [1].

Route `/mail/load_message_failures` was made in non-sudo as to take
ACLs into account, so that we don't get mail failures that we don't
have access [2]

However, checking ACLs on `mail.message` from `search` on
`mail.notification` is very slow [3], to the point where the RPC
takes minutes and results in a `memoryerror`.

Ideally we should have non-sudo and make checking ACLs more
performant. As a quick fix in a stable version, we revert to using
`sudo`, which results in same quick results as before.

[1]: https://github.com/odoo/odoo/pull/138330
[2]: https://github.com/odoo/odoo/pull/138330/files#diff-6be51f3695e69474a19cf6857370c8bb9b529a15d568952258cec9a0ae519fc4R23
[3]: https://github.com/odoo/odoo/blob/17.0/addons/mail/models/res_partner.py#L251

closes odoo/odoo#146184

Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>

addons/mail/controllers/webclient.py

@@ -20,4 +20,6 @@ class WebclientController(http.Controller):
 
     @http.route("/mail/load_message_failures", methods=["POST"], type="json", auth="user")
     def mail_load_message_failures(self):
-        return request.env.user.sudo(False).partner_id._message_fetch_failed()
+        # sudo as to not check ACL, which is far too costly
+        # sudo: res.users - return only failures of current user as author
+        return request.env.user.partner_id._message_fetch_failed()