Adds new route to show cleanup image tag settings

What does this MR do and why?

First MR to move container registry cleanup policies to a single page.

This adds a backend route for Move container registry cleanup policies to a s... (#363426 - closed) to render the cleanup policy form, however this MR will not be dealing with rendering the actual form.

After reading https://about.gitlab.com/handbook/product-development-flow/feature-flag-lifecycle/#when-to-use-feature-flags I decided this does not need a feature flag since navigating to this UI is not straight-forward. The user has to know the exact URL & even then, it should be safe since it is not rendering anything at the moment.

Screenshots or screen recordings

How to set up and validate locally

Enabled Container registry

1. Enable container registry in GDK
2. Login as admin
3. Visit any project.
4. Visit Settings > Packages & Registries on the sidebar & then append /cleanup_image_tags to the URL should return above screenshot.
5. Make sure clicking on the breadcrumb takes you to the right settings page

Disabled Container registry

1. Disable container registry in GDK
2. Login as admin
3. Visit any project.
4. Visit Settings > Packages & Registries on the sidebar & then append /cleanup_image_tags to the URL should return 404 page

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 #363426 (closed)