doc/csi: encourage deployment through Ceph-CSI Operator

Ceph-CSI ideally gets deployed by Ceph-CSI Operator, the other methods
(Helm Charts and Raw Manifests) are deprecated.

Include links to the newly published Ceph-CSI Operator documentation,
and mention NVMe-oF support as well.

Signed-off-by: Niels de Vos <ndevos@ibm.com>