feat: add reusable verify-boilerplate composite action

[Prachi01Yadav]

Fixes #1069

What this PR does

Adds a reusable composite GitHub Action at .github/actions/verify-boilerplate/ that wraps the existing hack/boilerplate/boilerplate.py script, so Kubeflow subprojects can enforce Apache 2.0 copyright headers without vendoring the script.

Requirements checklist

• Composite action wrapping hack/boilerplate/boilerplate.py — script is sourced directly from kubeflow/testing via actions/checkout with sparse-checkout, so callers never vendor it.
• Input for base ref — base-ref input defaults to the PR base branch (github.base_ref), so only changed/new files are flagged for year-less header enforcement.
• Input for boilerplate template directory — boilerplate-dir input lets repos with custom templates point to their own directory. Defaults to kubeflow/testing's templates.
• Sets up Python — includes a setup-python step (default 3.12) so callers don't need to add one.
• Non-zero exit on failure — the script already exits non-zero with remediation output; the action inherits this behavior.

Usage

Callers can use this action in their workflows like:

steps:
  - uses: actions/checkout@v4
    with:
      fetch-depth: 0

  - uses: kubeflow/testing/.github/actions/verify-boilerplate@master
    with:
      base-ref: ${{ github.base_ref }}

Context

• Tracking issue: request: Add Reusable copyright boilerplate check CI action #1069
• Related: chore: standardize copyright boilerplate and enforce with CI sdk#765, Standardize copyright boilerplate and enforce with CI workflow sdk#566

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[jaiakash]

@Prachi01Yadav please check the nit comments, rest looks good to me.

cc @tariq-hasan for review

[jaiakash]

/lgtm

[tariq-hasan]

I've just had a few additional comments. Overall lgtm. Thanks.

[Prachi01Yadav]

I've just had a few additional comments. Overall lgtm. Thanks.

@tariq-hasan Thanks for the review! I've applied all your suggestions (removed the checkout/cleanup steps and simplified the fallback). Let me know if everything looks good now!

[tariq-hasan]

Hi @Prachi01Yadav! I have added some further comments to help refine the first iteration and make it more robust.

[tariq-hasan]

Thanks @Prachi01Yadav!
/lgtm
/assign @jaiakash @juliusvonkohout @andreyvelich @nsingla

[tariq-hasan]

Depending on preference we can self-test this composite action directly on this testing repo (perhaps something like .github/workflows/code-quality-check.yaml) before there's adoption in consumer repos. Or we could test in kubeflow/sdk#765 directly.

[Prachi01Yadav]

Depending on preference we can self-test this composite action directly on this testing repo (perhaps something like .github/workflows/code-quality-check.yaml) before there's adoption in consumer repos. Or we could test in kubeflow/sdk#765 directly.

let's just test it directly in kubeflow/sdk#765, I can update that PR to use this action as soon as this is merged.. let me know if that sounds good to you