constructor (options = {}) {
    this.options = Object.assign(defaultOptions, options);
    this.fetch = fetch;
    this.rootUrl = `${this.options.protocol}://${this.options.hostname}:${this.options.port}/api/`;
  }
Create a SDK client.
@param {string} [port=5678] - DataHub port.
@param {string} [hostname='127.0.0.1'] - DataHub hostname.
@param {string} [protocol='http'] - DataHub protocol.