chore: make all file headers consistent

[alexandear]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

Fixes copyright headers for Go files and make it consistent. Integrates goheader linter to automatically check the file header.

Special notes for your reviewer:

Changes:

• Add missing file headers.
• Add missing year.
• Fix typos.

About goheader linter: https://golangci-lint.run/usage/linters/#goheader

Does this PR introduce a user-facing change?

NONE

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: alexandear
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[k8s-ci-robot]

Hi @alexandear. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[mbobrovskyi]

/ok-to-test

[mbobrovskyi]

/lgtm
Thanks!

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 8933e7facf8c998350ad3374258590a1f0e36e80

[tenzen-y]

Suggested change

	{{CopyrightDate}} The Kubernetes Authors.
	The Kubernetes Authors.

The current template without year is intended.
We drop the year since we want to avoid the license update every year: #1590

[tenzen-y]

Additionally, could we reuse this template instead of hardcoded one here?

https://github.com/kubernetes-sigs/kueue/blob/main/hack/boilerplate.go.txt

[alexandear]

I investigated PR #1590 before creating this one, and what I understood from the description is that it is only for generated code. This PR touches only human-added files, not the generated files.

In human-added files, there is no issue with updating the year every year. We add the year into license only on introducing a new file.

Are you sure I need to change the copyright template to be the same for human-added and generated files? It requires me to update roughly 6K files. It's not a big deal, just asking to be sure.

[alexandear]

@tenzen-y