Feat: sort `peekingduck nodes` output

[liyier90]

Closes https://github.com/aisingapore/PeekingDuck-Private/issues/111

• Adds a --order ASC/DESC option to sort peekingduck nodes output in either ascending or descending alphabetical order.
• Omit order argument in docstring to avoid duplication in CLI help message

Invoking 'peekingduck nodes --help'...
Usage: cli nodes [OPTIONS] [TYPE_NAME]

  Lists available nodes in PeekingDuck. When no argument is given, all
  available nodes will be listed. When the node type is given as an argument,
  all available nodes in the specified node type will be listed.

  Args:     type_name (str): input, augment, model, draw, dabble, or output.

Options:
  --order [ASC|DESC]  Sorts the node names by either ascending (ASC) or
                      descending (DESC) alphabetical order.

  --help              Show this message and exit.