Can be used to check the request parameters or perform authentication checks
@param {String} datasetId
@param {Object} params
@param {Object} params.query_params
@param {Object} params.meta_data
@param {Function} callback
function(datasetId, params, callback) {
      var interceptor = requestInterceptors[datasetId] || defaults.requestInterceptor;
      return interceptor(datasetId, params, callback);
    }