code: func (api *Client) LeaveChannelContext(ctx context.Context, channelID string) (bool, error) {
  	values := url.Values{
  		"token":   {api.token},
  		"channel": {channelID},
  	}
  
  	response, err := api.channelRequest(ctx, "channels.leave", values)
  	if err != nil {
  		return false, err
  	}
  
  	return response.NotInChannel, nil
  }
docs: // LeaveChannelContext makes the authenticated user leave the given channel with a custom context
  // see https://api.slack.com/methods/channels.leave