Update GitLab runner to use new registration token system

[Racer159]

Describe what should be investigated or refactored

The current way that we register runners is deprecated and will be removed in a future release of GitLab - we should update this to the new model and consider ways that we can improve the registration experience per #66 (if possible)

Links to any relevant code

#66

Additional context

This registration method should be available until v18 under feature flags but we should update this to avoid potential issues in the future.