helm: fail CI when values.yaml changes without a schema update

[kriyanshii]

Catch PRs that change Helm values but forget values.schema.json, as the first step of #536.

What was changed

Added a helm-lint CI step that runs hack/check-helm-values-schema.sh. The script fails when helm/temporal-worker-controller/values.yaml has non-comment changes in the PR and values.schema.json was not updated. Comment-only or whitespace-only edits are ignored.

This is the first of the two steps from #536 (detect drift). Auto-generating values.schema.json can follow in a later PR.

Why?

values.schema.json has been falling out of date when Helm values change. A CI check makes that mismatch visible on the PR instead of relying on reviewers to notice.

Checklist

1. Closes Detect drift in values.schema.json file #562

2. How was this tested:

   • ./hack/check-helm-values-schema.sh on this branch skips (no values.yaml change)
   • Adding newKey: true to values.yaml without touching the schema fails the script
   • Comment-only values.yaml changes still pass
   • Updating both files passes

3. Any docs updates needed?
   No. Schema generation is still manual; this PR only adds the check.

[jaypipes]

@kriyanshii awesome, thanks so much for the PR! I created a sub-issue (#562) specifically for the drift-detection and editing this PR summary to close out the sub-issue instead of the parent.