Create Praefect commands to list virtual storages and storages

Without dissecting the Praefect configuration, it is hard to tell for an admin what virtual storages and storages there are. This results in confusion which parameters are expected by commands when it says e.g. <virtual-storage>. It would probably help by quite a lot if we had commands which explicitly list only this information. E.g.

$ praefect -config /path/to/config list-virtual-storages
vs1
vs2
$ praefect -config /path/to/config list-storages -virtual-storage vs1
storage-1
storage-2
storage-3

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