chore(ci): block merge while api-deploy-required label is present (#46482)

## I have read the
[CONTRIBUTING.md](https://github.com/supabase/supabase/blob/master/CONTRIBUTING.md)
file.

YES

## What kind of change does this PR introduce?

CI / tooling — GitHub Actions workflow update.

## What is the current behavior?

PRs that modify `packages/api-types/types/**` can be merged before the
corresponding API has shipped to production, breaking the Studio
frontend when it calls endpoints that do not exist yet. The
`api-deploy-required` label is enforced only by convention and code
review, which is easy to miss.

## What is the new behavior?

- `.github/labeler.yml`: auto-applies `api-deploy-required` to any PR
that touches `packages/api-types/types/**`.
- `.github/workflows/label_prs.yml`: drops the `apps/docs/**/*` path
filter so the labeler runs on all PRs, and posts a one-time comment when
`api-deploy-required` is newly added (uses the labeler's `new-labels`
output so re-pushes do not re-comment).
- `.github/workflows/validate-pr.yml`: adds a step that fails the
`Validate pull request` check while the `api-deploy-required` label is
present, mirroring the existing `do-not-merge` pattern. The author
removes the label after confirming the API is live to unblock merge.

Reviewer: please confirm `Validate pull request` is configured as a
required check on `master` in branch protection — that step is what
enforces the block.

## Additional context

Resolves FE-3479

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Chores**
* Enhanced pull request automation with improved labeling rules for
API-related changes.
* Added validation that blocks pull request merging until API deployment
is confirmed for changes affecting API types.

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.github/workflows/validate-pr.yml

@@ -17,6 +17,12 @@ jobs:
           echo "PR blocked: [tag: do not merge]"
           exit 1
 
+      - name: Tagged with 'api-deploy-required'
+        if: contains( github.event.pull_request.labels.*.name, 'api-deploy-required')
+        run: |
+          echo "PR blocked: [tag: api-deploy-required] — confirm the API is deployed in production, then remove the label."
+          exit 1
+
       - name: All good
         if: ${{ success() }}
         run: |