### 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/qa/single-node-tests/src/javaRestTest/java/org/elasticsearch/xpack/transform/integration/TransformUpdateIT.java
"avg_rating": {
                    "avg": {
                      "field": "stars"
                    }
                  }
                },
                "max_page_search_size": 555
              }
            }""", transformDest, REVIEWS_INDEX_NAME);
        createTransformRequest.setJsonEntity(config);
        Map<String, Object> createTransformResponse = entityAsMap(client().performRequest(createTransformRequest));
        assertThat(createTransformResponse.get("acknowledged"), equalTo(Boolean.TRUE));
        Map<String, Object> transform = getTransformConfig(transformId, BASIC_AUTH_VALUE_TRANSFORM_USER);
        assertThat(XContentMapValues.extractValue("pivot.max_page_search_size", transform), equalTo(555));
        final Request updateRequest = createRequestWithAuth(
            "POST",
            getTransformEndpoint() + transformId + "/_update",
            BASIC_AUTH_VALUE_TRANSFORM_ADMIN_1
        );
        updateRequest.setJsonEntity("{}");
        Map<String, Object> updateResponse = entityAsMap(client().performRequest(updateRequest));
        assertNull(XContentMapValues.extractValue("pivot.max_page_search_size", updateResponse));
        assertThat(XContentMapValues.extractValue("settings.max_page_search_size", updateResponse), equalTo(555));
        transform = getTransformConfig(transformId, BASIC_AUTH_VALUE_TRANSFORM_USER);
        assertNull(XContentMapValues.extractValue("pivot.max_page_search_size", transform));
        assertThat(XContentMapValues.extractValue("settings.max_page_search_size", transform), equalTo(555));
    }
    public void testUpdateTransferRights() throws Exception {
        updateTransferRightsTester(false);
    }