code: function addApiVersionHeader(endpointRequest) {
    var api = endpointRequest.service.api;
    var apiVersion = api.apiVersion;
    if (apiVersion && !endpointRequest.httpRequest.headers['x-amz-api-version']) {
      endpointRequest.httpRequest.headers['x-amz-api-version'] = apiVersion;
    }
  }
docs: add api version header to endpoint operation
  @api private