Automatically find un-synchronised exercises that were once synchronised

[mk-mxp]

We did a great job at synchronising exercises up to now. To keep that level, we regularly should scan for news about the synchronised exercises:

• Add a curated list of already synchronised exercises
  • The list generated by configlet sync does not take into account quality changes we want to have during synchronisation
  • I think we need more of these / similar lists when we start raising the next quality bar (e.g. auto-generated by test-generator, optimized for Test Driven Development etc.)
  • Once we synchronised all existing exercises, we can use find to generate the list to work through
• Add a scheduled GitHub action to scan for synchronisation state of exercises from that list
  • Run configlet sync for the exercise
  • When changes are required, open a GitHub issue (expect < 1 per week, see .github/workflows/no-important-files-changed.yml)
  • Alternatively prepare a PR with the changes introduced by configlet sync (see .github/workflows/configlet-generate.yml for doing a commit)