Allow 'Request a Demo' query param on Sales page

1. Change Summary

Allow 'Request a Demo' query param on Sales page

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/sales/?contact-topic=request-demo	https://allow-demo-query-param-on-sales-page.about.gitlab-review.app/sales/?contact-topic=request-demo	Screenshot

3. Deployment Steps

[List key deployment steps or configurations]