Introduce `OrderInstructions` Message

[mistermoe]

Context

Currently, a Quote contains both payin and payout instructions which Alice can use to facilitate a payin or receive a payout. This introduces non-deterministic outcomes because Alice can actually facilitate a pay in prior to sending an Order message.

Proposal

We should consider moving payment instructions from the Quote message to a new message kind, OrderInstructions, which is sent by the PFI after Alice submits an Order message.

Message Contents

Data

field	data type	required	description
payin	PaymentInstruction	Y	the amount of payin currency that the PFI will receive
payout	PaymentInstruction	Y	the amount of payout currency that Alice will receive

PaymentInstruction

field	data type	required	description
link	String	N	Link to allow Alice to pay PFI, or be paid by the PFI
instruction	String	N	Instruction on how Alice can pay PFI, or how Alice can be paid by the PFI

Example

{
  "metadata": {...},
  "data": {
    "payin": {
      "link": "some_payment_link",
      "instruction": "plain_text"
    },
    "payout": {
      "link": "some_payment_link",
      "instruction": "plain_text"
    }
  }
}