### 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
}
    }
    /**
     * Handle new settings at runtime, this is triggered by a call to _transform/id/_update
     *
     * @param newSettings The new settings that should be applied
     */
    public void applyNewSettings(SettingsConfig newSettings) {
        auditor.info(transformConfig.getId(), "Transform settings have been updated.");
        logger.info("[{}] transform settings have been updated.", transformConfig.getId());
        docsPerSecond = newSettings.getDocsPerSecond() != null ? newSettings.getDocsPerSecond() : -1;
        if (Objects.equals(newSettings.getMaxPageSearchSize(), initialConfiguredPageSize) == false) {
            configurePageSize(newSettings.getMaxPageSearchSize());
        }
        rethrottle();
    }
    @Override
    protected void onFailure(Exception exc) {
        startIndexerThreadShutdown();
        
        try {
            handleFailure(exc);
        } catch (Exception e) {
            logger.error(() -> "[" + getJobId() + "] transform encountered an unexpected internal exception: ", e);
        }
    }
    @Override
    protected void onStop() {
        auditor.info(transformConfig.getId(), "Transform has stopped.");
        logger.info("[{}] transform has stopped.", transformConfig.getId());