Downsampling is broken. Not sure why yet (likely caused by #97557). Invoking the downsample api results into:

```
org.elasticsearch.ElasticsearchSecurityException: no indices permissions found
        at org.elasticsearch.xpack.core.security.support.Exceptions.authorizationError(Exceptions.java:32) ~[?:?]
        at org.elasticsearch.xpack.core.security.authz.accesscontrol.SecurityIndexReaderWrapper.getIndicesAccessControl(SecurityIn
dexReaderWrapper.java:110) ~[?:?]
        at org.elasticsearch.xpack.core.security.authz.accesscontrol.SecurityIndexReaderWrapper.apply(SecurityIndexReaderWrapper.j
ava:76) ~[?:?]
        at org.elasticsearch.xpack.core.security.authz.accesscontrol.SecurityIndexReaderWrapper.apply(SecurityIndexReaderWrapper.j
ava:46) ~[?:?]
        at org.elasticsearch.index.shard.IndexShard.wrapSearcher(IndexShard.java:1590) ~[elasticsearch-8.11.0-SNAPSHOT.jar:?]
        at org.elasticsearch.index.shard.IndexShard.wrapSearcher(IndexShard.java:1561) ~[elasticsearch-8.11.0-SNAPSHOT.jar:?]
        at org.elasticsearch.index.engine.Engine$SearcherSupplier.acquireSearcher(Engine.java:1321) ~[elasticsearch-8.11.0-SNAPSHO
T.jar:?]
        at org.elasticsearch.index.engine.Engine.acquireSearcher(Engine.java:774) ~[elasticsearch-8.11.0-SNAPSHOT.jar:?]
        at org.elasticsearch.index.shard.IndexShard.acquireSearcher(IndexShard.java:1549) ~[elasticsearch-8.11.0-SNAPSHOT.jar:?]
        at org.elasticsearch.xpack.downsample.DownsampleShardIndexer.<init>(DownsampleShardIndexer.java:115) ~[?:?]
        at org.elasticsearch.xpack.downsample.DownsampleShardPersistentTaskExecutor.startDownsampleShardIndexer(DownsampleShardPersistentTaskExecutor.java:111) ~[?:?]
        at org.elasticsearch.xpack.downsample.DownsampleShardPersistentTaskExecutor$1.doRun(DownsampleShardPersistentTaskExecutor.java:87) ~[?:?]
        at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun(ThreadContext.java:983) ~[elasticsearch-8.11.0-SNAPSHOT.jar:?]
        at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:26) ~[elasticsearch-8.11.0-SNAPSHOT.jar:?]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144) ~[?:?]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642) ~[?:?]
        at java.lang.Thread.run(Thread.java:1623) ~[?:?]
```
x-pack/plugin/downsample/src/main/java/org/elasticsearch/xpack/downsample/DownsampleShardIndexer.java
private static final Logger logger = LogManager.getLogger(DownsampleShardIndexer.class);
    public static final int DOWNSAMPLE_BULK_ACTIONS = 10000;
    public static final ByteSizeValue DOWNSAMPLE_BULK_SIZE = new ByteSizeValue(1, ByteSizeUnit.MB);
    public static final ByteSizeValue DOWNSAMPLE_MAX_BYTES_IN_FLIGHT = new ByteSizeValue(50, ByteSizeUnit.MB);
    private final IndexShard indexShard;
    private final Client client;
    private final String downsampleIndex;
    private final Engine.Searcher searcher;
    private final SearchExecutionContext searchExecutionContext;
    private final DateFieldMapper.DateFieldType timestampField;
    private final DocValueFormat timestampFormat;
    private final Rounding.Prepared rounding;
    private final List<FieldValueFetcher> fieldValueFetchers;
    private final DownsampleShardTask task;
    private final DownsampleShardPersistentTaskState state;
    private volatile boolean abort = false;
    ByteSizeValue downsampleBulkSize = DOWNSAMPLE_BULK_SIZE;
    ByteSizeValue downsampleMaxBytesInFlight = DOWNSAMPLE_MAX_BYTES_IN_FLIGHT;
    DownsampleShardIndexer(
        final DownsampleShardTask task,
        final Client client,
        final IndexService indexService,
        final ShardId shardId,
        final String downsampleIndex,
        final DownsampleConfig config,