Onboarding experiment group edit progress bar

What does this MR do?

Modify the group edit page's progress bar from the subscription checkout flow for the onboarding issues experiment.

When in the experiment, the checkout page should show the progress bar with the following steps:

1. Your Profile
2. Checkout
3. Your GitLab group
4. Your first project

Parent issue: gitlab-org/growth/product#107 (closed)

Screenshots