docs: update Ceph upgrade docs for 1.6
docs: update Ceph upgrade docs for 1.6

Signed-off-by: Blaine Gardner <135b86f2968bdbcc730c10d8ababd343bb675986@redhat.com>

rook/rook,rook/nfs,rook/rook,rook/nfs,rook/rook,rook/nfs,rook/rook,rook/rook