**Elasticsearch version** (`bin/elasticsearch --version`): 7.16 (earlier too), 8.0, 8.1

**Description of the problem including expected versus actual behavior**:
Currently, the rollover requests are not cancellable, irrespective of the underlying incoming HTTP channel being closed (eg. by a proxy). This could result in clients receiving `504` and retrying the rollovers, resulting in multiple rollover operations being processed (some products issue rollovers without specifying conditions, so this could translate in multiple subsequent rollovers being executed).

This proposes using the `RestCancellableNodeClient` infrastructure for the rollover API, such that elasticsearch can react to the incoming HTTP connection being closed by cancelling the rollover operation.

server/src/test/java/org/elasticsearch/action/admin/indices/rollover/TransportRolloverActionTests.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.action.admin.indices.rollover;
import org.elasticsearch.Version;
import org.elasticsearch.action.ActionListener;
import org.elasticsearch.action.ActionRequest;
import org.elasticsearch.action.admin.indices.stats.CommonStats;
import org.elasticsearch.action.admin.indices.stats.IndexStats;
import org.elasticsearch.action.admin.indices.stats.IndicesStatsAction;
import org.elasticsearch.action.admin.indices.stats.IndicesStatsResponse;
import org.elasticsearch.action.admin.indices.stats.IndicesStatsTests;
import org.elasticsearch.action.admin.indices.stats.ShardStats;
import org.elasticsearch.action.support.ActionFilters;
import org.elasticsearch.action.support.PlainActionFuture;
import org.elasticsearch.client.internal.Client;
import org.elasticsearch.cluster.ClusterName;
import org.elasticsearch.cluster.ClusterState;
import org.elasticsearch.cluster.metadata.AliasMetadata;