After a customer has paid via an Adyen terminal, the Adyen server sends
a request containing the payment confirmation to the webhook on the odoo
server.
At the moment, the pos frontend continuously polls the backend in order
to find out whether or not the confirmation from Adyen arrived.
This pattern is wasteful and over complicated.
In this PR I replace the polling logic with websockets communication.
closesodoo/odoo#125593
Task: 3342693
Signed-off-by: Joseph Caburnay (jcb) <jcb@odoo.com>