Update logo for new user onboarding

What does this MR do and why?

Uses brand_image instead of old tanuki logo

• default to new tanuki if no logo set

What does this MR not do?

The new version doesn't have a hat 🤷

Screenshots or screen recordings

Before	After

How to set up and validate locally

• Simulate SaaS
• Create a new user and go through onboarding flow (http://localhost:3000/new-group/new-project/-/learn_gitlab/onboarding)

UX Paper Cuts 16.5 → Cleanup (#424403 - closed)