Onboarding experiment new project step

What does this MR do?

Add a create your first project page for the onboarding issues experiment. (design)

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

There is no changelog, since all changes from this MR are behind the experiment onboarding_issues, which is controlled by the feature flag onboarding_issues_experiment_percentage.

Note: This MR depends on and targets !31952 (merged). I will update the target branch to master once !31952 (merged) has been merged.

Screenshots

Create tab	Import tab