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/index/IndexRequest.java
/**
     * Sets the document source to index.
     *
     * Note, its preferable to either set it using {@link #source(org.elasticsearch.common.xcontent.XContentBuilder)}
     * or using the {@link #source(byte[], XContentType)}.
     */
    public IndexRequest source(String source, XContentType xContentType) {
        return source(new BytesArray(source), xContentType);
    }
    /**
     * Sets the content source to index.
     */
    public IndexRequest source(XContentBuilder sourceBuilder) {
        return source(BytesReference.bytes(sourceBuilder), sourceBuilder.contentType());
    }
    /**
     * Sets the content source to index using the default content type ({@link Requests#INDEX_CONTENT_TYPE})
     * <p>
     * <b>Note: the number of objects passed to this method must be an even
     * number. Also the first argument in each pair (the field name) must have a
     * valid String representation.</b>
     * </p>
     */
    public IndexRequest source(Object... source) {
        return source(Requests.INDEX_CONTENT_TYPE, source);
    }
    /**
     * Sets the content source to index.
     * <p>
     * <b>Note: the number of objects passed to this method as varargs must be an even