docs: def config_add(self, key, value, **kwargs):
          """
          Add a value to a key.
  
          Returns a list of warnings Conda may have emitted.
          """
          cmd_list = ['config', '--add', key, value]
          cmd_list.extend(self._setup_config_from_kwargs(kwargs))
  
          return self._call_and_parse(
              cmd_list,
              abspath=kwargs.get('abspath', True),
              callback=lambda o, e: o.get('warnings', []))