Ensure files have copyright headers

[SaschaSchwarze0]

At the moment, many files in this repository do not have a copyright header. This needs to be fixed. Ideally, we also have an action that verifies the presence of those headers through an action during pull request validation.

Some infrastructure from the build repo to copy: https://github.com/shipwright-io/build/blob/main/hack/generate-copyright.sh

[adambkaplan]

/kind cleanup

[adambkaplan]

This kind of script would be a good candidate for a shared "build machinery" repository. OpenShift has something like this: https://github.com/openshift/build-machinery-go