### Description

ShutdownShardMigrationStatus serializes ShardAllocationDecision, which, as of #97803, is chunked. ShardAllocationDecision grows with the number of nodes. Therefore, it would save heap space to chunk ShutdownShardMigrationStatus as well.
server/src/main/java/org/elasticsearch/cluster/metadata/ShutdownShardMigrationStatus.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 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */
package org.elasticsearch.cluster.metadata;
import org.elasticsearch.TransportVersion;
import org.elasticsearch.TransportVersions;
import org.elasticsearch.cluster.routing.allocation.ShardAllocationDecision;
import org.elasticsearch.common.Strings;
import org.elasticsearch.common.io.stream.StreamInput;
import org.elasticsearch.common.io.stream.StreamOutput;
import org.elasticsearch.common.io.stream.Writeable;
import org.elasticsearch.common.xcontent.ChunkedToXContent;
import org.elasticsearch.core.Nullable;
import org.elasticsearch.xcontent.ToXContentObject;
import org.elasticsearch.xcontent.XContentBuilder;
import java.io.IOException;
import java.util.Objects;
public class ShutdownShardMigrationStatus implements Writeable, ToXContentObject {
    private static final TransportVersion ALLOCATION_DECISION_ADDED_VERSION = TransportVersions.V_7_16_0;
    public static final String NODE_ALLOCATION_DECISION_KEY = "node_allocation_decision";