### 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
}
    public Map<String, String> getFieldMappings() {
        return fieldMappings;
    }
    public TransformProgress getProgress() {
        return progress;
    }
    public TransformCheckpoint getLastCheckpoint() {
        return lastCheckpoint;
    }
    public TransformCheckpoint getNextCheckpoint() {
        return nextCheckpoint;
    }
    public CheckpointProvider getCheckpointProvider() {
        return checkpointProvider;
    }
    /**
     * Request a checkpoint
     */
    protected void createCheckpoint(ActionListener<TransformCheckpoint> listener) {
        checkpointProvider.createNextCheckpoint(
            getLastCheckpoint(),
            ActionListener.wrap(
                checkpoint -> transformsConfigManager.putTransformCheckpoint(
                    checkpoint,
                    ActionListener.wrap(putCheckPointResponse -> listener.onResponse(checkpoint), createCheckpointException -> {
                        logger.warn(() -> "[" + getJobId() + "] failed to create checkpoint.", createCheckpointException);
                        listener.onFailure(
                            new RuntimeException(
                                "Failed to create checkpoint due to: " + createCheckpointException.getMessage(),