refactor(vdev): replace manifest generation script with native command

[pront]

Summary

Motivation

Kubernetes manifest generation still lives in a shell script behind vdev build manifests. Move it into vdev so chart-version arguments are parsed directly and the release workflow no longer depends on scripts/generate-manifests.sh.

Changes

• Replace the script with a native command that pins one Helm chart version, rejects downgrades, and regenerates all three manifest variants, READMEs, and kustomization resource lists.
• Keep Helm and yq for rendering and YAML cleanup, and finish rendering every variant before replacing existing files.
• Update the Make target to pass --chart-version directly and bump vdev to 0.3.27 so CI installs the new implementation.

References

Prerequisite to #26469, which removes the remaining script-wrapper macro.

How did you test this PR?

• Ran the old script and the new command with real Helm and yq against chart 0.58.0: all 22 generated files matched byte-for-byte, and a second native run was unchanged.
• Passed all 228 vdev tests, including coverage for explicit/default chart versions, downgrade rejection, retries, and preserving existing manifests on Helm or yq failure. Git configuration was isolated for tests that create temporary repositories.

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-05T18:07:37.081576Z	5f85186	Draft marked ready
🔒 Security Review	✅ Completed 2026-10-05T18:10:04.843024Z	5f85186	Draft marked ready

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[datadoghq-integration]

More details

The native command preserves the former generator’s release wiring and completes all Helm renders before replacing checked-in manifests; no actionable regression was identified.

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