**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
.put(IndexMetadata.SETTING_INDEX_UUID, UUIDs.randomBase64UUID())
            .put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)
            .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 0)
            .build();
        return IndexMetadata.builder(indexName)
            .creationDate(System.currentTimeMillis() - TimeValue.timeValueHours(3).getMillis())
            .settings(settings)
            .build();
    }
    private static Condition<?> createTestCondition() {
        final Condition<?> condition = mock(Condition.class);
        when(condition.evaluate(any())).thenReturn(new Condition.Result(condition, true));
        return condition;
    }
    public static IndicesStatsResponse randomIndicesStatsResponse(final IndexMetadata[] indices) {
        List<ShardStats> shardStats = new ArrayList<>();
        for (final IndexMetadata index : indices) {
            int numShards = randomIntBetween(1, 3);
            int primaryIdx = randomIntBetween(-1, numShards - 1); 
            for (int i = 0; i < numShards; i++) {
                ShardId shardId = new ShardId(index.getIndex(), i);
                boolean primary = (i == primaryIdx);
                Path path = createTempDir().resolve("indices").resolve(index.getIndexUUID()).resolve(String.valueOf(i));
                ShardRouting shardRouting = ShardRouting.newUnassigned(
                    shardId,
                    primary,
                    primary ? RecoverySource.EmptyStoreRecoverySource.INSTANCE : RecoverySource.PeerRecoverySource.INSTANCE,
                    new UnassignedInfo(UnassignedInfo.Reason.INDEX_CREATED, null)
                );
                shardRouting = shardRouting.initialize("node-0", null, ShardRouting.UNAVAILABLE_EXPECTED_SHARD_SIZE);