HashiCorp legal now requires a copyright claim in a comment at the top of
every substantial file in this repository. If we don't add this ourselves
then a bot will open a PR to add missing entries, but that process adds
git history, pull request, and GitHub notification noise so instead we'll
deal with it proactively as part of our usual code generation steps.
This means that pull requests will fail their checks if there are any
files that lack copyright headers, so we can deal with those before we
merge rather than in a subsequent PR.
