Automatically create PRs to tracks when fetch script(s) change

[ErikSchierboom]

Whenever the scripts/fetch-configlet or scripts/fetch-configlet.ps1 scripts change, we should automatically submit a PR to all the tracks that contain those file(s).

Small note: some tracks might have renamed the script to fetch_configlet or fetch_configlet.sh or fetch-configlet.sh. This is probably okay, as long as our automatic update script recognizes these alternative names.