@Override
    public void getConfig(DocumentProtocolPoliciesConfig.Builder builder) {
        for (ContentCluster cluster : Content.getContentClusters(repo)) {
            DocumentProtocolPoliciesConfig.Cluster.Builder clusterBuilder = new DocumentProtocolPoliciesConfig.Cluster.Builder();
            addSelector(cluster.getConfigId(), cluster.getRoutingSelector(), clusterBuilder);
            addRoutes(getDirectRouteName(cluster.getConfigId()), getIndexedRouteName(cluster.getConfigId()), clusterBuilder);
            builder.cluster(cluster.getConfigId(), clusterBuilder);
        }
    }
Creates a service index based on the plugins loaded. This means to fill the index with all services known by this
protocol by traversing the plugins.

@param plugins All initialized plugins of the Vespa model
@return the index of all known services
config-model/src/main/java/com/yahoo/vespa/model/routing/DocumentProtocol.java