private int eventIndexAt(Instant at) {
        for (int i = 0; i < scalingEvents.size(); i++) {
            if (scalingEvents.get(i).at().equals(at))
                return i;
        }
        return -1;
    }
Add or update (based on "at" time) a scaling event
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/applications/Cluster.java