Strip JS comment steps from submit/apply; add github-decision + artifact upload

[Mpdreamz]

The three actions/github-script comment steps and their four JS scripts are removed from changelog/submit/apply. Commenting now happens in the downstream release-notes-comments workflow (added in #323). A new shell step records the commit outcome into the metadata and uploads it as changelog-decision so the comment workflow picks it up.

Affects: Release notes, Automation

Why

Commenting from inside submit/apply required pull-requests: write on the commit job. The JS scripts (post-success-comment.js, post-comment-only.js, post-failure-comment.js) were the only things in the repo that posted PR comments. Moving them to a dedicated workflow_run job with its own token gives the commit job a narrower permission set and lets any future consumer opt into comments by copying one file instead of modifying the submit workflow. The three steps also lacked continue-on-error: true, so a transient 403 from the GitHub API could fail a run that otherwise committed the entry successfully.

What

JS scripts removed

All four scripts in changelog/submit/apply/scripts/ (comment-helper.js, post-success-comment.js, post-comment-only.js, post-failure-comment.js) are deleted. The config input — used only by post-failure-comment.js — is also removed from the composite.

Record decision and stage comment artifact step

After the commit step, a single shell step runs if: always() with continue-on-error: true. It copies the staging metadata and generated YAML into .artifacts/changelog-decision/, calls changelog github-decision --commit-outcome <committed|failed|none> to stamp the outcome, and sets --committed-file when the commit succeeded. The directory layout matches what changelog github-comment expects.

Upload decision artifact step

Uploads .artifacts/changelog-decision as changelog-decision with if: always() and continue-on-error: true, if-no-files-found: ignore. The downstream release-notes-comments workflow (PR #323) picks this up with pull-requests: write and posts or updates the sticky comment.

Verify

Open a PR in a repo that has release-notes-comments.yml wired up. The Changelog submit workflow should complete without posting a comment itself. A few seconds later the Changelog PR comments workflow should run and post (or update) the sticky ### 📋 Changelog comment.

Stack: 3 of 4, on top of #323. PR 4 drops should-comment-success / should-comment-failure from docs-builder once this PR is merged and no code reads those outputs.

Risk: elastic/cloud currently reads should-comment-success and should-comment-failure from submit/apply/evaluate-artifact. Those outputs are on ChangelogArtifactEvaluationService, not apply. They are dropped in the coordinated docs-builder PR 4 — this PR does not touch them.

Out of scope: changelog/submit/evaluate is untouched. changelog-submit.yml is untouched. elastic/cloud's consumer workflow must have release-notes-comments.yml in place on its default branch before this PR is merged.