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
sizeInBytes += (request.source() != null ? request.source().length() : 0) + REQUEST_OVERHEAD;
        indices.add(request.index());
        return this;
    }
    /**
     * Adds an {@link UpdateRequest} to the list of actions to execute.
     */
    public BulkRequest add(UpdateRequest request) {
        return internalAdd(request);
    }
    BulkRequest internalAdd(UpdateRequest request) {
        Objects.requireNonNull(request, "'request' must not be null");
        applyGlobalMandatoryParameters(request);
        requests.add(request);
        if (request.doc() != null) {
            sizeInBytes += request.doc().source().length();
        }
        if (request.upsertRequest() != null) {
            sizeInBytes += request.upsertRequest().source().length();
        }
        if (request.script() != null) {
            sizeInBytes += request.script().getIdOrCode().length() * 2;
        }
        indices.add(request.index());
        return this;
    }
    /**
     * Adds an {@link DeleteRequest} to the list of actions to execute.
     */
    public BulkRequest add(DeleteRequest request) {