[pH] ask contributors use copyright header "The Kubeflow Authors"

[Bobgy]

After #5587,
we should stick to "The Kubefow Authors" copyright header.

But people may miss the new convention,

Proposal:

1. p0 add another PR checklist to educate contributors
2. p2 add presubmit (not sure how we can actually achieve that)

[Bobgy]

presubmit can be implemented by using addlicense go CLI tool and then verify no changes have been made

Also we can recommend "Copyright Inserter" vscode plugin: https://marketplace.visualstudio.com/items?itemName=minherz.copyright-inserter

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically closed because it has not had recent activity. Please comment "/reopen" to reopen it.