[POS Service] POST `/payment` route

[njlie]

The POS Service needs to extend a POST /payment route that will handle the the creation of an incoming payment with the POS service's Rafiki backend, acquire the Card Service URL from the card's wallet address, and then use the resulting incomingPaymentUrl and cardService values to create a request to the Card Service using the POS Services' Card service client…service.

The route will then forward the result of the Card Service Client call to the POS device as the response.

# POST /payment
## Request Body
{
  card: {
    walletAddress: string
    trasactionCounter: number
    expiry: Date
  }
  signature: string # Card signature
}

## Response Body
### 200 OK
{
  result: "approved"
}

### 401 Unauthorized
{
  result: "card_expired" || "invalid_signature"
}