doc: add in-tree volume to csi migration usage doc
doc: add in-tree volume to csi migration usage doc

This commit adds in-tree to csi volume migration usage documentation
to the examples.

Signed-off-by: Humble Chirammal <dc8ba7e82a7df22725dedec9b10c7aaab9ec713f@redhat.com>

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