Whats new pages for previous versions

1. Change Summary

• Moves each version file into its own page
• Edits decap config
• Does not include dropdown or email field - Those are in separate issues
• Removes the filtering logic as per the request in figma

2. QA Checklist

[This merge request should follow all best practices utilizing our team code standards and our project's development documentation]

• Code Cleanup: Any messages, linter warnings, and/or deprecation warnings are cleaned up in the console
• Tech Debt: I have created, or documented, any fast follow-up work that needs to be done after this MR is merged
• Common Component Regression Check: I have verified all impacted pages of my common component updates have been checked for regressions and UX is aware of any wider-scoped visual changes
• Efficient Code Review: I have tested and reviewed my own changes thoroughly before assigning a reviewer
• Accessibility: Axe tools run and issues addressed
• Cross-browser compatibility: Works on Safari, Chrome, and Firefox
• Analytics and SEO: Compatible with Google Analytics and SEO tools
• Localization checked for regressions
• I have run window.optimizely.get('state').getExperimentStates() on my affected pages and verified no active experiments are targeting these pages.

[Provide concise steps to test the changes]

Review App

Production	Review app	Screenshot
https://about.gitlab.com/fr-fr/releases/whats-new/#18.1 (example of a translated version thats still live)	https://1506-whats-new-versions.about.gitlab-review.app/releases/whats-new/18-1/	(all languages, all versions)

3. Deployment Steps

[List key deployment steps or configurations]

Closes #1506 (closed)