This reverts commit 1f264575.

This makes it possible to run the script to validate all links manually, via a button on the GitHub Actions panel. This will be useful for testing and when you need to run validation right away.

Changes:

- It is now possible to only check for duplicate
  links (without checking if the links are working)

- Check for duplicate links when a push occurs

- Update the scripts documentation accordingly

fixing the broken contributing guide link

Co-authored-by: Yann Bertrand <5855339+yannbertrand@users.noreply.github.com>

This reverts commit 03d96f8a.