### Description

Currently, when we execute retention policy, we also refresh the destination index by setting:
```
setRefresh(true)
```
on the DBQ request.
This can cause permission errors which are surprising to the user as the permissions are not required when the transform starts:
```
task encountered irrecoverable failure: org.elasticsearch.ElasticsearchSecurityException: action [indices:admin/refresh] is unauthorized for user [found-internal-kibana4-server] with roles [kibana_system,found-internal-kibana4-server] on indices [logs-cloud_security_posture.findings_latest-default], this action is granted by the index privileges [maintenance,manage,all]
```

We still want the user to have the permissions to delete the documents. But we should execute `refresh` as the system user.
x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/transforms/TransformIndexer.java
private void startIndexerThreadShutdown() {
        synchronized (context) {
            indexerThreadShuttingDown = true;
            saveStateRequestedDuringIndexerThreadShutdown = false;
        }
    }
    private void finishIndexerThreadShutdown() {
        synchronized (context) {
            indexerThreadShuttingDown = false;
            if (saveStateRequestedDuringIndexerThreadShutdown) {
                
                
                if (context.shouldStopAtCheckpoint() && nextCheckpoint == null) {
                    stop();
                }
                doSaveState(getState(), getPosition(), () -> {});
            }
        }
    }
    /**
     * Thrown when the transform configuration disappeared permanently.
     * (not if reloading failed due to an intermittent problem)
     */
    static class TransformConfigLostOnReloadException extends ResourceNotFoundException {
        TransformConfigLostOnReloadException(String msg, Throwable cause, Object... args) {
            super(msg, cause, args);
        }
    }
}