Add Chromium-only Playwright image publisher (#94051)
### What?
Add the Next.js-owned Chromium-only Playwright image definition and a
workflow that builds and pushes it to GHCR.
### Why?
This needs to merge before the reusable CI workflow starts using the
image, so the GHCR tag exists when job containers are initialized.
### How?
- Add a Noble-based Chromium image with the CI build dependencies,
Playwright Chromium, and the repository's Node.js LTS version
preinstalled.
- Add a manual/canary-only publisher workflow that derives Playwright
from `package.json`, Node.js from `build_reusable.yml`, and tags images
with a Next.js-owned revision suffix.
- Keep the image revision in the publisher workflow so Dockerfile-only
changes can publish a distinct immutable tag.
### Verification
- `git diff --cached --check`
- `ruby -e 'require "yaml";
YAML.load_file(".github/workflows/playwright_chromium_image.yml")'`
- Not run: `docker buildx build --check --build-arg
PLAYWRIGHT_VERSION=1.58.2 .github/images/playwright-chromium` (Docker
daemon is not running locally)
- Not run: `pnpm prettier --with-node-modules --ignore-path
.prettierignore --write .github/workflows/playwright_chromium_image.yml
.github/images/playwright-chromium/Dockerfile` (`prettier` command is
not available in this checkout)
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