### 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
hasSourceChanged = hasChanged;
                if (hasChanged) {
                    context.setChangesLastDetectedAt(instantOfTrigger);
                    logger.debug("[{}] source has changed, triggering new indexer run.", getJobId());
                    changedSourceListener.onResponse(null);
                } else {
                    logger.trace("[{}] source has not changed, finish indexer early.", getJobId());
                    
                    listener.onResponse(false);
                }
            }, failure -> {
                
                
                hasSourceChanged = true;
                listener.onFailure(failure);
            }));
        } else {
            hasSourceChanged = true;
            context.setLastSearchTime(instantOfTrigger);
            context.setChangesLastDetectedAt(instantOfTrigger);
            changedSourceListener.onResponse(null);
        }
    }
    protected void initializeFunction() {
        
        function = FunctionFactory.create(getConfig());
        if (isContinuous()) {
            changeCollector = function.buildChangeCollector(getConfig().getSyncConfig().getField());
        }
    }