Create a cache sweeper

[jcoyne]

We're currently using a file cache. A big portion of this cache only is valid for 1 hour (https://github.com/sul-dlss/purl/blob/main/config/settings.yml#L15). In order to free up space we need to periodically run Rails.cache.cleanup. Create a cron job that runs ever night that does this. This will need to happen on both app machines -a/-b since the filesystem is not shared.