docs: update ceph external cluster flags
docs: update ceph external cluster flags

Some optional Flags are already added
for external script but not documented,
So to expose the functionality to users
adding them to the doc list

Signed-off-by: parth-gr <583be16d1c64273f0f691248fe7345d86bf42e7d@redhat.com>

rook/rook,rook/rook,rook/rook,rook/rook,rook/rook