docs: clean-up Ceph NFS Gateway CRD
docs: clean-up Ceph NFS Gateway CRD

- fixup RADOS pool name to match what is used by the CRD
- add missing RADOS namespace to the Sample description
- move/merge description of the RADOS pool/namespace config into the
  sample text instead of inline comments within the CRD yaml
- add inline code block for `spec.server.active` field

Signed-off-by: Michael Fritch <c02b41e756731fcea1863ef09dc53c3c4d2e1cc8@suse.com>

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