Self Managed: Show default onboarding flow for SM

What does this MR do and why?

This MR ensures that the default onboarding flow for SM admins is not affected. Since they go through a different onboarding process, having the homepage set as default for those folks will not result in the expected behavior as what they are used to of.

In this case, this ensures the onboarding stays as the default unless they explicitly decide to change it.

References

Screenshots or screen recordings

Before for SM users:

After for SM users:

How to set up and validate locally

Example:

1. export GITLAB_SIMULATE_SAAS=0
2. in the rails console do the following:

  admin = User.find_by(username: 'root')
  Feature.enable(:personal_homepage, admin)
  admin.members.destroy_all
  admin.project_authorizations.delete_all

3. Check that when logged in as admin, you will be redirected to the onboarding screen.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.