Track the continuous onboarding iteration 2 experiment

What does this MR do and why?

Adds the requested amount of tracking for the Continuous Onboarding iteration 2 experiment.

Screenshots or screen recordings

https://youtu.be/5apVqc1z2os

How to set up and validate locally

1. Ensure you have an EE license applied to your GDK
2. Activate billing plans & trials for your local install
3. Install Snowplow Micro and set it up to work in development
4. Make sure these feature flags are enabled:
   • Feature.enable(:add_namespace_and_project_to_snowplow_tracking)
   • Feature.enable(:change_continuous_onboarding_link_urls)
5. Register for a new user account, which should land you on the “Learn GitLab” dashboard
6. Try out the links, notice where they take you and check what events are sent to Snowplow Micro

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #343581 (closed) & #337534 (closed)