Use a example project for user onboarding

Overview

The onboarding MVC in https://gitlab.com/gitlab-org/gitlab-ce/issues/57832 will start with walking a new user through GitLab CE. This is a good MVC for validating the approach, but we need to have a greater control over the experience.

Proposal

• Instead of walking through GitLab CE, walk through an imported project specific to the onboarding exercise.
• The project should be simple (HTML static site) with some seed data to show off issues and MRs.
• For GitLab.com, we could have the project spin up as a configured GitLab Page with a configured .gitlab-ci.yml so we can demonstrate CI/CD live during the walkthrough.
• The example/templated project should be easy to tear down, but this could be a future iteration.