updateHeaders(parsedEvent) {
    if (this.getStopReason(parsedEvent) === null) {
      return
    }

    this.response.response.headers = {
      'x-amzn-requestid': this.passThroughParams.response.response.headers['x-amzn-requestid']
    }
    delete parsedEvent['amazon-bedrock-invocationMetrics']
  }
If the given event is the last event in the stream, update the response
headers with the metrics data from the event.

@param {object} parsedEvent