..., pos_self_order_bancontact_pay

---

Bancontact changed the issuer of their callbacks from "payconiq" to
"Payconiq". Since our signature verification checked against the old
lowercase value, every callback was rejected, so the terminal never
received the customer's payment confirmation. We have also added more
logs diagnose similar issues more easily in the future.

While fixing this, we found the signature check could be bypassed
entirely: passing `mode=test` in the callback URL skipped verification
altogether, so an attacker could forge their own unsigned callback just
by adding it. Signature verification is now always performed,
regardless of mode.

On top of that, the webhook only checked that the JWS subject matched
the caller-supplied `ppid`, never that this ppid actually belonged to
the targeted POS config - both being plain URL parameters, an attacker
with their own Bancontact account could point its own validly signed
callback at a victim's config_id and finalize its pending payment
instead. We replace `ppid`/`mode` with `payment_method_id` in the
callback URL, and derive the expected ppid and preprod/production
environment from that record server-side, checking it's actually
configured on the target POS config before relaying the callback.

Finally, guard the kiosk and register client-side handlers, and the
webhook itself, against reprocessing an already-finalized payment,
closing the impact of a replayed callback.

---

Task: https://www.odoo.com/odoo/project/1737/tasks/6449864

Forward-Port-Of: odoo/odoo#279417