docs: public void purchaseReservedInstance(String instanceId, int reservationLength, String reservationTimeUnit) {
          this.purchaseReservedInstance(new PurchaseReservedInstanceRequeset()
                  .withInstanceId(instanceId)
                  .withBilling(new Billing().withReservation(new Reservation()
                                  .withReservationLength(reservationLength)
                                  .withReservationTimeUnit(reservationTimeUnit))));
      }