Follow-up from "Implement group-level dependency list export API"

The following discussion from !123397 (merged) should be addressed:

• @bwill started a discussion: (+1 comment)

  Suggestion (non-blocking): We're loading all dependencies into memory here. For large group hierarchies, this has potential for memory exhaustion. Looking at Dependencies::ExportService, I think we could mitigate the risk of this by writing data to the export file in a stream. I would suggest that we do so before enabling the feature flag on .com.