private double peakLoad(Load.Dimension dimension) {
        double total = 0;
        int count = 0;
        for (var nodeTimeseries : timeseries) {
            OptionalDouble value = nodeTimeseries.peak(dimension);
            if (value.isEmpty()) continue;
            total += value.getAsDouble();
            count++;
        }
        if (count == 0) return 0;
        return total / count;
    }
Returns the "peak load" in this: Which is for each load dimension,
the average of the highest reading for that dimension on each node.
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/autoscale/ClusterNodesTimeseries.java