static ZooKeeperDiscoverySpec serverSets() {
        return serverSets(ServerSetsInstance::serviceEndpoint);
    }
Returns a {@link ZooKeeperDiscoverySpec} that is compatible with
<a href="https://twitter.github.io/finagle/docs/com/twitter/serverset.html">Finagle ServerSets</a>.

@see ZooKeeperRegistrationSpec#builderForServerSets()
zookeeper3/src/main/java/com/linecorp/armeria/client/zookeeper/ZooKeeperDiscoverySpec.java