rook: Use helm to install rook-based Ceph storage stack

This requires at least rook v1.7 (and therefore #417 (closed) ).

Carefully evaluate how and if we should add a migration path and helmificate rook.

https://github.com/rook/rook/blob/master/Documentation/helm.md#helm-charts

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information