Add Ceph-csi Upgrade documentation
Add Ceph-csi Upgrade documentation

Added Upgrade doc from v1.2.x to v2.0.0

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

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