FederationConfig.Target.Builder getTargetConfig() {
            FederationConfig.Target.Builder tb = new FederationConfig.Target.Builder();
            tb.id(id.stringValue()).useByDefault(targetOptions.getUseByDefault());
            getSearchChainsConfig(tb);
            return tb;
        }
One or more search chains that are handled as a single group,
which can be federated to as a single entity.
config-model/src/main/java/com/yahoo/vespa/model/container/search/searchchain/FederationSearcher.java