docs: def render_build_args(options, ns):
      """Get docker build args dict, rendering any templated args.
  
      Args:
      options (dict):
          The dictionary for a given image from chartpress.yaml.
          Fields in `options['buildArgs']` will be rendered and returned,
          if defined.
      ns (dict): the namespace used when rendering templated arguments
      """
      build_args = options.get('buildArgs', {})
      for key, value in build_args.items():
          build_args[key] = value.format(**ns)
      return build_args