Cancel a queued number order

Cancels an order that is still queued (pending) - no body, returns the order with status cancelled. Nothing is charged (the fee is only deducted once the number is ready) and an account that has never topped up can order again. An order being provisioned right now (provisioning) cannot be cancelled - it returns 409 in_progress, try again in a few minutes; neither can a done or failed one (409 invalid_transition) - release a finished number with DELETE /v1/numbers/{e164} instead. Cancelling an already cancelled order is harmless (it is returned unchanged).