Default to Import tab experiment

What does this MR do and why?

Based on the inputted answer on Step 4 of registration I'm signing up for GitLab because: (i.e. JTBD = Job to be done), we should default them to Import instead of Create on Step 6 of registration

Screenshots or screen recordings

https://gitlab.com/gitlab-org/gitlab/-/issues/431405#control-vs-candidate-experience

How to set up and validate locally

bin/rails console

Feature.enable(:default_to_import_tab)

• Setup gdk to simulate SaaS - https://docs.gitlab.com/ee/development/ee_features.html#simulate-a-saas-instance and restart GDK
• Sign out. Visit /users/sign_up. Submit the form.
• On the welcome page select:
• I'm signing up for GitLab because: - I want to store my code, Just me and Create a new project.
• Submit the form. Make sure Create tab is active.
• Finish registration. Sign out.
• Visit /users/sign_up. Submit the form.
• On the welcome page select:
• I'm signing up for GitLab because: - I want to move my repository to GitLab from somewhere else, Just me and Create a new project.
• Submit the form. Make sure Import tab is active.

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.

Related to #431405