Add backend route for virtual registry cleanup policy

What does this MR do and why?

Add backend route to show virtual registry cleanup policy form.

Introduce beta feature flag ui_for_virtual_registry_cleanup_policy

Adds feature specs.

EE: true

References

• This route will eventually implement #548566[MVC_CleanupPolicy.png]
• How does cleanup work link will be added in UI: Implement virtual registry cleanup policy form (#577289)

Screenshots or screen recordings

Before	After
404 page

How to set up and validate locally

1. In the rails console, run Feature.enable(:ui_for_virtual_registry_cleanup_policy)
2. Visit /groups/<root-group-path>/-/settings/packages_and_registries/virtual_registry_cleanup_policy
3. Confirm that route is available.
4. Visit Group > Settings > Packages and registries.
5. Toggle off Virtual registry
6. Confirm that route /groups/<root-group-path>/-/settings/packages_and_registries/virtual_registry_cleanup_policy is not available anymore.
7. Toggle on Virtual registry

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #578145