Answer
No — there's no supported way to have a certificate file automatically pulled from Harvest and copied into the import folder as part of AutoBuilder or delivery creation. It's also worth reconsidering the approach even if it were technically possible: storing secrets like certificates in source control is a bad practice generally, since anyone with access to that source code repository would then be able to view (and potentially modify) them. Certificate deployment needs to stay a manual, per-environment step rather than something folded into the automated build/delivery pipeline.