Redirect new signups to the project path instead of the tutorial paths

What does this MR do and why?

Redirects new signups to the project path instead of the tutorial paths.

The Getting Started and Learn GitLab experiences have low usage and were not positively received during UX research. Rather than landing new users on a tutorial checklist, they should land directly on their project overview page where they can start exploring GitLab naturally

References

#599757+

How to set up and validate locally

1. Ensure GDK is running in SaaS mode export GITLAB_SIMULATE_SAAS=1
2. Enable the feature flag in Rails console: Feature.enable(:remove_onboarding_tutorial_pages)
3. Create a fresh user and go through the signup flows on /users/sign_up and /-/trial_registrations/new (register → welcome → group/project creation). After project creation you should land on the project overview page instead of the Get Started / Learn GitLab page.

MR acceptance checklist

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