Add periodic job for contributor-site Hugo modules update

[TineoC]

This PR adds periodic and presubmit Prow jobs for kubernetes/contributor-site.

• Periodic Job: Updates Hugo modules weekly and opens a PR.
• Presubmit Job: Validates Hugo module updates on PRs to ensure no breaking changes.

This replaces the previous GitHub Actions proposal in kubernetes/contributor-site#647.

Depends-on: kubernetes/contributor-site#647
/sig contributor-experience
/area prow
/kind feature

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: TineoC
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Details

Needs approval from an approver in each of these files:

• config/OWNERS
• config/jobs/kubernetes/sig-k8s-infra/trusted/OWNERS

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[TineoC]

@lmktfy

[TineoC]

Local dry-run test output (arm64)
Ran ./hack/update-hugo-modules.sh --dry-run locally on darwin/arm64:

$ ./hack/update-hugo-modules.sh --dry-run
hugo mod get -u
hugo mod tidy
Validating the build...
Start building sites …
hugo v0.133.0-c9777473d1369f812d727a6c07dc57ad7be7bf62+extended darwin/arm64 BuildDate=2024-08-17T19:57:41Z

                   | EN
-------------------+------
  Pages            | 923
  Paginator pages  |   6
  Non-page files   | 88
  Static files     | 37
  Processed images |   3
  Aliases          |   9
  Cleaned          |   0

Total in 43898 ms
No module updates found. Exiting.

[TineoC]

Update: Pinned image tag

Replaced :latest with :v0.133.0-7f658d63039e for reproducible builds.

The tag is derived from Hugo version (0.133.0) + a 12-char hash of build-relevant files (Dockerfile, Makefile, netlify.toml, go.mod, go.sum, etc.). It will need updating when the contributor-site image is rebuilt.