Use learn gitlab utlimate template for experiment

What does this MR do?

Issue: #322026 (closed)

During onboarding, we create a "learn gitlab" project for the user. Before this change: We used the learn_gitlab template, for our "Learn Gitlab Page" experiment. With this MR we use the learn_gitlab_ultimate_trial template.

The reason: we want to link to issues that are only available in the ultimate project template (code owners and merge request approvals)

No changelog because it's behind the feature flag learn_gitlab_a_experiment_percentage and learn_gitlab_b_experiment_percentage

If you want to check out the Learn GitLab page experiment locally

• Enable one of the feature flags: Feature.enable_percentage_of_time(:learn_gitlab_b_experiment_percentage, 100)
• Signup with a new user
• Go to the "Learn Gitlab" or any other project
• Click on "Learn Gitlab"

Screenshots (strongly suggested)

Learn Gitlab Page	List of issues

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team