code: func (api *Client) GetChannelRepliesContext(ctx context.Context, channelID, thread_ts string) ([]Message, error) {
  	values := url.Values{
  		"token":     {api.token},
  		"channel":   {channelID},
  		"thread_ts": {thread_ts},
  	}
  	response, err := api.channelRequest(ctx, "channels.replies", values)
  	if err != nil {
  		return nil, err
  	}
  	return response.History.Messages, nil
  }
docs: // GetChannelRepliesContext gets an entire thread (a message plus all the messages in reply to it) with a custom context
  // see https://api.slack.com/methods/channels.replies