### Elasticsearch Version

main

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

MacOS

### Problem Description

When there are 2 or more concurrent `_update` requests issued, one of them may fail with `ResourceAlreadyExistsException` exception which is misleading.


### Steps to Reproduce

1. Spawn a number of `_update` requests at the same time
2. Look at the results of these requests
3. Observe `ResourceAlreadyExistsException` being thrown in the case of conflict

### Logs (if relevant)

_No response_
x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/persistence/IndexBasedTransformConfigManager.java
SearchAction.INSTANCE,
            searchRequest,
            ActionListener.<SearchResponse>wrap(searchResponse -> {
                if (searchResponse.getHits().getHits().length == 0) {
                    if (allowNoMatch) {
                        resultListener.onResponse(null);
                    } else {
                        resultListener.onFailure(
                            new ResourceNotFoundException(
                                TransformMessages.getMessage(TransformMessages.UNKNOWN_TRANSFORM_STATS, transformId)
                            )
                        );
                    }
                    return;
                }
                SearchHit searchHit = searchResponse.getHits().getHits()[0];
                BytesReference source = searchHit.getSourceRef();
                try (
                    InputStream stream = source.streamInput();
                    XContentParser parser = XContentFactory.xContent(XContentType.JSON)
                        .createParser(xContentRegistry, LoggingDeprecationHandler.INSTANCE, stream)
                ) {
                    resultListener.onResponse(
                        Tuple.tuple(TransformStoredDoc.fromXContent(parser), SeqNoPrimaryTermAndIndex.fromSearchHit(searchHit))
                    );
                } catch (Exception e) {
                    logger.error(
                        TransformMessages.getMessage(TransformMessages.FAILED_TO_PARSE_TRANSFORM_STATISTICS_CONFIGURATION, transformId),
                        e
                    );