function getFlowResultFilenamePrefix(flowResult) {
  const lhr = flowResult.steps[0].lhr;
  const name = flowResult.name.replace(/\s/g, '-');
  return getFilenamePrefix(name, lhr.fetchTime);
}
Generate a filenamePrefix of name_YYYY-MM-DD_HH-MM-SS.
@param {{name: string, steps: Array<{lhr: {fetchTime: string}}>}} flowResult
@return {string}