### 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
@Override
    protected Response createTestInstance() {
        String randomPrefix = randomAlphaOfLength(5);
        List<LifecyclePolicyResponseItem> responseItems = new ArrayList<>();
        for (int i = 0; i < randomIntBetween(0, 2); i++) {
            responseItems.add(
                new LifecyclePolicyResponseItem(
                    randomTestLifecyclePolicy(randomPrefix + i),
                    randomNonNegativeLong(),