Document setting Docker image version dynamically (JS)

[karlhorky]

The container image version can be kept up to date with the Playwright version in package.json with configuring a previous GitHub Actions job, as documented in the following resources:

• https://github.com/karlhorky/repro-dynamic-playwright-container-image
• https://github.com/karlhorky/playwright-tricks#sync-playwright-version-from-packagejson-to-github-actions-container-image
• [Question]: How to cache on github actions? #7249 (comment)

Alternatives Considered

1. This could be an addition to the existing "Via Containers" section, with examples for all languages Node.js, Python, Java, .NET
2. This new workflow could become the default suggested "Via Containers" workflow for GitHub Actions
3. A separate GitHub Actions workflow to edit the versions in the workflow files and commit to Git (downsides: more PR noise and greater required GitHub permissions)