Interact with ASE on Payment Pointer request

[sabineschaller]

The Payment pointer GET request will publish a webhook to the ASE. Then, the ASE will do a payment pointer lookup on their own system, and be able to createPaymentPointer.

That means payment pointer information does not necessarily have to be stored within Rafiki anymore. On a GET request to the payment pointer, the request is forwarded to the ASE that populates the payment pointer details, and asyncronously creates the payment pointer (on the fly)

[mkurapov]

...synchronous hook to the ASE to request additional information.

Maybe "additional information" is not necessary to specify here since it's basically about replacing payment pointer storage altogether