Authenticate the GitLab Duo usage controller

What does this MR do and why?

Adds the necessary safeguards to the GitLab Duo usage controller.

note: Accessing the page anonymously, you would only see the GitLab Duo empty state. No data about the group's usage would be exposed.

Changelog: fixed
EE: true

MR acceptance checklist

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

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Run your GDK in SaaS mode: https://docs.gitlab.com/ee/development/ee_features.html#simulate-a-saas-instance.
2. Navigate to a top-level group that has an Ultimate license.
3. There should be a Setting > GitLab Duo menu item that brings to a dedicated page to manage the feature's usage.

Related to #464019