Create a payment route

Opens a route in one of two directions. **`onramp`** opens a deposit account in `sourceCurrency`; whatever lands there is paid out as stablecoin to `destinationAddress`. **`offramp`** opens a deposit address on `sourcePaymentRail`; stablecoin sent there is paid out as fiat to the bank account described in the request. The required bank fields depend on `destinationCurrency` and `destinationPaymentRail` — see the guide. Off-ramp is enabled separately from on-ramp, and the company must have been activated by AlphaX before any route can be opened.