When BulkProcessor retries failed item requests then the same `IndexRequest` instance are used in a new `BulkRequest` for a retry. This is a problem when `BulkProcessor` is used from within Elasticsearch (this is the case for deprecation index logging, ilm/slm history and more), because the bulk request transport action may have set the `autoGeneratedTimestamp` field. 

If that is the case then error such a these may appear in the logs and the `BulkProcessor` retry fails:

```
Bulk write of 1 deprecation logs failed: autoGeneratedTimestamp should not be set externally
java.lang.IllegalArgumentException: autoGeneratedTimestamp should not be set externally
	at org.elasticsearch.action.bulk.TransportBulkAction.doInternalExecute(TransportBulkAction.java:223) ~[elasticsearch-7.16.1.jar:7.16.1]
	at org.elasticsearch.action.bulk.TransportBulkAction$1.doRun(TransportBulkAction.java:192) ~[elasticsearch-7.16.1.jar:7.16.1]
	at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:26) [elasticsearch-7.16.1.jar:7.16.1]
	at org.elasticsearch.action.bulk.TransportBulkAction.doExecute(TransportBulkAction.java:200) [elasticsearch-7.16.1.jar:7.16.1]
	at org.elasticsearch.action.bulk.TransportBulkAction.doExecute(TransportBulkAction.java:91) [elasticsearch-7.16.1.jar:7.16.1]
```

In the bulk transport action, for each bulk item request of the `BulkRequest` its `process()` method is invoked. Incase of `IndexRequest` when no _id has been specified an id is generated and in that case the `IndexRequest#autoGeneratedTimestamp ` field is set. If the bulk request fails at a later stage, for example because there was no capacity on the node that hosts a primary shard to index documents then the bulk response will contain a `EsRejectedExecutionException` exception in the `BulkResponse` for the bulk items this failure occurred for. This is normal behaviour. However the `BulkProcessor` has retry logic and `EsRejectedExecutionException` is deemed retry-able. The `BulkProcessor` [reuses the same bulk request item instances ](https://github.com/elastic/elasticsearch/blob/master/server/src/main/java/org/elasticsearch/action/bulk/Retry.java#L139)(`IndexRequest` in this case) upon retry. This causes the failure mentioned in the stack trace.
server/src/main/java/org/elasticsearch/action/bulk/BulkRequest.java
}
    /**
     * Adds a framed data in binary format
     */
    public BulkRequest add(byte[] data, int from, int length, @Nullable String defaultIndex, XContentType xContentType) throws IOException {
        return add(new BytesArray(data, from, length), defaultIndex, xContentType);
    }
    /**
     * Adds a framed data in binary format
     */
    public BulkRequest add(BytesReference data, @Nullable String defaultIndex, XContentType xContentType) throws IOException {
        return add(data, defaultIndex, null, null, null, null, true, xContentType, RestApiVersion.current());
    }
    /**
     * Adds a framed data in binary format
     */
    public BulkRequest add(BytesReference data, @Nullable String defaultIndex, boolean allowExplicitIndex, XContentType xContentType)
        throws IOException {
        return add(data, defaultIndex, null, null, null, null, allowExplicitIndex, xContentType, RestApiVersion.current());
    }
    public BulkRequest add(
        BytesReference data,
        @Nullable String defaultIndex,
        @Nullable String defaultRouting,
        @Nullable FetchSourceContext defaultFetchSourceContext,
        @Nullable String defaultPipeline,
        @Nullable Boolean defaultRequireAlias,
        boolean allowExplicitIndex,
        XContentType xContentType,
        RestApiVersion restApiVersion