doc: add document for rbd snapshot and clone
doc: add document for rbd snapshot and clone

Added a document which contains the steps
and RBD CLI commands we execute when we create
a kubernetes snapshot, delete kubernetes snapshot,
Restore a snapshot to a new PVC,Kubernetes volume
cloning and kubernetes PVC deletion.

Signed-off-by: Madhu Rajanna <60fbf37a92c2a0908e31296d18dadbec5a4dae17@gmail.com>

ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi