Update object storage label to support virtual registries

🫳 Context

In Maven virtual registry MVC (API only interactions) (&14137 - closed), we're working towards the first iteration of the Maven virtual registry.

This feature is part of the Category:Virtual Registry which was renamed from Category:Dependency Proxy.

Regarding object storage resources, the virtual registries are using the same resources as the dependency proxy for container images.

As such, in the object storage usage page (of a root group), we have a section for Dependency proxy. This MR updates the label of that section to include the virtual registries.

🤔 What does this MR do and why?

• In the storage usage breakdown page (of a root group), the label for Dependency proxy will now take into account virtual registries.
  • The More information link is kept as-is for now. Once we have the first pages for the virtual registry documentation, we will update this part.
• Update the related specs.

Since virtual registries are still behind a WIP feature flag, the label change is gated behind that feature flag too.

📚 References

Please include cross links to any resources that are relevant to this MR. This will give reviewers and future readers helpful context to give an efficient review of the changes introduced.

• #480360 (comment 2265042120)
• #480360 (closed)

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Before	After

⚙️ How to set up and validate locally

1. Have a root group ready.
2. Navigate to /-/usage_quotas#storage-quota-tab of that root group.
3. Notice that the label is Local proxy used for frequently-accessed upstream Docker images..
4. In a rails console: Feature.enable(:virtual_registry_maven). Restart GDK if necessary.
5. Notice that the label is now Cache for frequently-accessed Docker images and packages..