Update product_metrics schema fragments to test_kitchen

Clare Mingrequested to merge
T407901/rename-product-metrics-fragments into master

As part of the re-name/brand to Test Kitchen, this MR adds a new subdirectory in fragments called test_kitchen which mirrors active schema fragments from product_metrics and makes a major version bump (2.0.0 in nearly every case).

Taking the opportunity here to remove the experiments fragment which is being deprecated in favor of experiment.

Merge request checklist

  • Phabricator task(s) associated with this change added to commit message (use Bug: TASK_NUMBER on line at end of commit message)
  • [N/A] wikitech:Event Platform/Instrumentation How To#Writing MediaWiki instrumentation code was followed for the schema(s) in the merge request. This includes if this merge request entails a new MEDIUM or HIGH risk schema, or if this merge request entails a schema alteration that increases the risk level based on Data Collection Guidelines.
  • [N/A] If this introduces a new or upgraded MEDIUM or HIGH risk level, @sguebo added as a reviewer (please check @sguebo calendar for availability and find an alternate if @sguebo is out).
  • wikitech:Event Platform/Schemas/Guidelines was followed for the schema(s) in the merge request.
  • [N/A] Links to any other data specifications, such as a measurement plan or instrumentation specification if pertinent. Links to related code / Gerrit/GitLab patch pertinent to this schema change if it exists yet; if it doesn't exist yet that is okay and the merge requester should be sure to ensure reachability for that code via the commit message's referenced Phabricator task(s) later on. Please add links for any data specifications and relevant patches below this checkbox line if you have them.

Bug: T407901

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