private static Set<String> presentClusters(SearchChains searchChains) {
        Set<String> presentClusters = new LinkedHashSet<>();
        for (LocalProvider provider : searchChains.localProviders()) {
            presentClusters.add(provider.getClusterName());
        }
        return presentClusters;
    }
Adds default search chains for all local clusters not mentioned explicitly
@author Tony Vaagenes
config-model/src/main/java/com/yahoo/vespa/model/container/search/searchchain/defaultsearchchains/LocalClustersCreator.java