### 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
pageSize = function.getInitialPageSize();
            
            if (changeCollector != null) {
                changeCollector.clear();
            }
            long checkpoint = context.incrementAndGetCheckpoint();
            lastCheckpoint = getNextCheckpoint();
            nextCheckpoint = null;
            
            context.resetReasonAndFailureCounter();
            
            
            
            
            
            
            if (progress.getPercentComplete() != null && progress.getPercentComplete() < 100.0) {
                progress.incrementDocsProcessed(progress.getTotalDocs() - progress.getDocumentsProcessed());
            }
            if (lastCheckpoint != null) {
                long docsIndexed = progress.getDocumentsIndexed();
                long docsProcessed = progress.getDocumentsProcessed();
                long durationMs = System.currentTimeMillis() - lastCheckpoint.getTimestamp();
                getStats().incrementCheckpointExponentialAverages(durationMs < 0 ? 0 : durationMs, docsIndexed, docsProcessed);
            }
            if (shouldAuditOnFinish(checkpoint)) {
                auditor.info(getJobId(), "Finished indexing for transform checkpoint [" + checkpoint + "].");
            }
            logger.debug("[{}] finished indexing for transform checkpoint [{}].", getJobId(), checkpoint);