Consider using OSUOSL's s3-compatible storage

I noticed that https://overlookinfratech.com/downloads/ points to https://yum.overlookinfratech.com/ now, but when I first looked it pointed to https://yum.overlookinfratech.com/ (and is still simply a CNAME).

We can also consider using this instead of hosting our own webserver. It may be an issue to set the right caching headers, but I haven't looked at that.