public Autoscaling.Metrics metrics() {
        Instant now = clock.instant();
        return new Autoscaling.Metrics(averageQueryRate(now).orElse(0),
                                       growthRateHeadroom(now),
                                       cpu(now).costPerQuery().orElse(0));
    }
Returns the ideal load across the nodes of this such that each node will be at ideal load
if one of the nodes go down.
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/autoscale/ClusterModel.java