"Garbage collect" ZarrArchives

From the [design doc](https://github.com/dandi/dandi-archive/blob/master/doc/design/garbage-collection-1.md):
> ZarrArchives may be large enough that deleting automatically may result in fairly catastrophic data loss, so no automatic garbage collection should be done. Instead, ZarrArchives that have not been modified in more than 30 days should be logged for manual review.

and hence the air quotes.