Support for --puppeteer-script

[patrickhulce]

Usage:

lhci collect --puppeteer-script=./path/to/script.js

// This function is invoked before the first run of each URL under test
module.exports = async (browser, urlUnderTest, allCollectOptions) => {
  if (!urlUnderTest.includes('/app')) return;

  const page = await browser.newPage();
  await page.goto('http://localhost:3000/login');
  await page.type('#username', 'test_user');
  await page.type('#password', 'password');
  await page.click('button');
  await page.waitFor('.welcome-logged-in-user');
}

[connorjclark]

Should there be a similar construct for setting / tweaking the LH config based on the URL? For example, I am imagining wanting to clear cache in the general case, but for one URL set up auth and disable cache clearing.