Draft: Redesigning free trial page

What does this MR do and why?

We would like to update the Free Trial Sign-Up screen styles, which will improve the customer experience as measured by conversion rate.

closes: https://gitlab.com/gitlab-com/marketing/digital-experience/buyer-experience/-/issues/2243

Screenshots or screen recordings

New Design

How to set up and validate locally

1. Enable feature flag :restyle_login_page
2. Enable terms and conditions
3. Enable login with github
4. Visit Free Trial

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.