Exit registration verification

What does this MR do and why?

This adds an Exit link to the required verification page, when the require_verification_for_namespace_creation experiment is enabled, which allows the user to skip credit card verification and group + project creation during signup. It can be toggled through a feature flag.

Issue: https://gitlab.com/gitlab-org/growth/team-tasks/-/issues/559

Screenshots or screen recordings

How to set up and validate locally

1. Enable the combined_registration experiment

   Feature.enable(:combined_registration)

2. Enable the require_verification_for_namespace_creation experiment

   Feature.enable(:require_verification_for_namespace_creation)

3. Enable the exit_registration_verification feature flag

   Feature.enable(:exit_registration_verification)

4. Visit the combined registration page: http://localhost:3000/users/sign_up/groups_projects/new

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.