Pipeline Empty State Experiment: Show Hello World CI template

What does this MR do?

Issue: gitlab-org/growth/team-tasks#310 (closed)

This is an experiment to list CI templates when there is no CI set up for a project yet. In this MR we add a new section for a "Hello World" template, which also gets added with this MR. This Hello World template is really just printing out "Hello World" but should get our users an easy way to try out CI/CD.

Description	MR
List templates in empty pipeline state	!57286 (merged)
Add "Hello World" template to empty pipeline experiment	👈 you are here

How to test locally

Note: There might be a bit of a caching issue with feature flags & experiments that other reviewers already experienced that requires restarting the gdk if you want to check out both versions.

• Checkout branch
  • git fetch origin nicolasdular/hello-world-ci-template
  • git checkout nicolasdular/hello-world-ci-template
• yarn
• echo 'Feature.enable(:pipeline_empty_state_templates)' | bin/rails c
• Create or go to a project without a .gitlab-ci.yml
• Disabled "Default to Auto DevOps pipeline" in the CI/CD settings of your project (http://localhost:3000/<group_name>/<project_name>/-/settings/ci_cd
• Go to CI/CD -> Pipelines (http://localhost:3000/<group_name>/<project_name>/-/pipelines

Screenshots (strongly suggested)

Control	Candidate

Flow

Desktop	Mobile	Clicking on a template

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• 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