code: public Optional<AlertPolicyChannel> update(long policyId, long channelId)
      {
          QueryParameterList queryParams = new QueryParameterList();
          queryParams.add("policy_id", policyId);
          queryParams.add("channel_ids", channelId);
          return HTTP.PUT("/v2/alerts_policy_channels.json", null, null, queryParams, ALERT_POLICY_CHANNEL);
      }
docs: Adds the given alert channel to the alert policy with the given id.
  @param policyId The id of the alert policy to add the channel to
  @param channelId The id of the alert channel to add
  @return The alert policy channel that was updated