static ServerSetsRegistrationSpecBuilder builderForServerSets() {
        return new ServerSetsRegistrationSpecBuilder();
    }
Returns a new {@link ServerSetsRegistrationSpecBuilder}. The specification is compatible with
<a href="https://twitter.github.io/finagle/docs/com/twitter/serverset.html">Finagle ServerSets</a>.

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