[Split from CAA-96]

Once we get support for uploading layered formats like XCF (CAA-105), it'd be nice if those could be automatically exported to 300ppi JPEG by the server. This beats having Picard do it because, e.g., a 280MB XCF easily becomes as 700K JPEG — saving Picard having to download almost 280MB.

(And of course it beats the person uploading doing it because it's less work for the uploader).