private void recordCurrentStateInHistoryAtTime(final long currentTimeMs) {
        clusterStateHistory.add(currentClusterState, currentTimeMs);
    }
Returns the last state provided to updateLatestCandidateStateBundle, which _may or may not_ be
a published state. Primary use case for this function is a caller which is interested in
changes that may not be reflected in the published state. The best example of this would
be node state changes when a cluster is marked as Down.
clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/StateVersionTracker.java