Set up Ceph RGW

Depends on #3 (closed)

Because Ceph uses a binary object store internally, it has the ability to expose an HTTP API that functions exactly like S3 storage. Ceph calls this "Rados Gateway", or radosgw, or rgw, and it is an optional component of a Ceph system.

While block devices are useful for many kinds of workloads, especially when they can be provisioned, object storage is hugely useful for all sorts of data siloing, as S3 has demonstrated. Installing RGW to expose the Ceph backend would provide this to cluster-internal clients without needing to pay for S3, and potentially to external clients (via reverse proxy).