feat(v2): adding support for multiple experiments, audiences and campaigns per page

[ramboz]

This is a complete rewrite of the engine to support multiple experiments, audiences and campaigns per page, as well as hiding configurations behind named sheets.

Features:

• Add support for multiple experiments, audiences and campaigns per page (1 at the page level, 1 for each section, and n for fragments/blocks).
• Add support for specifying a manifest as config for each leveraging hidden sheets so the configs are not exposed by default
• Expose new JS API to track what experiments/audiences/campaigns were applied to the page:
  • window.hlx.experiments/window.hlx.audiences/window.hlx.campaigns which are JS arrays containing the page modification details. The format is:

    {
      type: /* one of "page", "section" or "fragment" */,
      el: /* the DOM element the changes applied to (body, section or fragment) */,
      servedExperience: /* the URL for the content that was inlined for that page modification */,
      config: { /* experiment/campaign/audience details */ },
    }

  • the old singular equivalents (i.e.window.hlx.experiment) are still around for backward compatibility but will only contain the page-level type modifications
• Expose a new DOM Event with experiment/audience/campaign details for easy integration with reporting or third-party libs

  document.addEventListener('aem:experimentation', (ev) => console.log(ev.detail));
  /* The event details will contain:
     - type: one of 'experiment', 'audience' or 'campaign',
     - element: the DOM element that was modified,
     - the experiment and variant name, the audience name, or the campaign name
  */

• Add E2E tests and code coverage reporting

BREAKING CHANGE:

• The (undocumented) full-experiments setup via external manifest has been removed, and replaced by fragment-level experiences
• Remove support for <meta property="…"> meta tags since only the <meta name="…"/> are used
• Remove sampling rate adjustments in favor of feat(minirum): allow increasing the sampling rate up to 1/10 for specific use cases helix-rum-js#159 to guarantee data integrity in RUM

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