public SELF rampingUpInterval(Duration rampingUpInterval) {
        requireNonNull(rampingUpInterval, "rampingUpInterval");
        return rampingUpIntervalMillis(rampingUpInterval.toMillis());
    }
Sets the interval between weight updates during ramp up.
{@value DEFAULT_RAMPING_UP_INTERVAL_MILLIS} millis is used by default.
core/src/main/java/com/linecorp/armeria/common/loadbalancer/AbstractRampingUpLoadBalancerBuilder.java