### 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.
x-pack/plugin/shutdown/src/main/java/org/elasticsearch/xpack/shutdown/GetShutdownStatusAction.java
public static final GetShutdownStatusAction INSTANCE = new GetShutdownStatusAction();
    public static final String NAME = "cluster:admin/shutdown/get";
    public GetShutdownStatusAction() {
        super(NAME, Response::new);
    }
    public static class Request extends MasterNodeRequest<Request> {
        private final String[] nodeIds;
        public Request(String... nodeIds) {
            this.nodeIds = nodeIds;
        }
        public static Request readFrom(StreamInput in) throws IOException {
            return new Request(in.readStringArray());
        }
        @Override
        public void writeTo(StreamOutput out) throws IOException {
            out.writeStringArray(this.nodeIds);
        }
        public String[] getNodeIds() {
            return nodeIds;
        }
        @Override
        public ActionRequestValidationException validate() {
            return null;
        }
        @Override
        public boolean equals(Object o) {