### Description

Clusters can have thousands of ILM policies. 
`GET _ilm/policy` returns all of them and runs on the master node.

This proposes we chunk the response for better memory usage and clients experience.

Relates to https://github.com/elastic/elasticsearch/issues/96568
x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/ilm/action/GetLifecycleResponseTests.java
/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0; you may not use this file except in compliance with the Elastic License
 * 2.0.
 */
package org.elasticsearch.xpack.core.ilm.action;
import org.elasticsearch.cluster.metadata.ItemUsage;
import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
import org.elasticsearch.common.io.stream.Writeable;
import org.elasticsearch.core.Nullable;
import org.elasticsearch.test.AbstractWireSerializingTestCase;
import org.elasticsearch.xpack.core.ilm.LifecycleAction;
import org.elasticsearch.xpack.core.ilm.LifecycleType;
import org.elasticsearch.xpack.core.ilm.MockAction;
import org.elasticsearch.xpack.core.ilm.TestLifecycleType;
import org.elasticsearch.xpack.core.ilm.action.GetLifecycleAction.LifecyclePolicyResponseItem;
import org.elasticsearch.xpack.core.ilm.action.GetLifecycleAction.Response;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import static org.elasticsearch.xpack.core.ilm.LifecyclePolicyTests.randomTestLifecyclePolicy;
public class GetLifecycleResponseTests extends AbstractWireSerializingTestCase<Response> {