Free trial registration redesign experiment

What does this MR do and why?

• Redesign the Free Trial Registration page in hopes that it will improve the customer experience as measured by conversion rate.
• Use GLEX experiment for the redesign
• shared partials were created to enable keeping a SSOT in the form and other areas that are currently used in 3 different areas: sign up, trial registration control, trial registration candidate.

related to: https://gitlab.com/gitlab-org/gitlab/-/issues/429111

Screenshots or screen recordings

control	candidate

How to set up and validate locally

1. Simulate SaaS and restart GDK
2. Navigation to the /-/trial_registrations/new (http://gdk.test:3000/-/trial_registrations/new) and the control will be displayed
3. To see the candidate use command Feature.enable(:free_trial_registration_redesign) in the rails console

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.