Fix welcome and phone page dead loop on SaaS

relate https://jihulab.com/gitlab-cn/gitlab/-/issues/3455

analyze

1. visit welcome page, redirect to phone page due to filter :enforce_phone_verification!
2. visit phone page, redirect to welcome page due to filter onboarding_redirect
3. dead loop

solution

1. skip filter onboarding_redirect when visit phone page in order to break dead loop