Add container registry to Namespace usage quotas page

What does this MR do and why?

Displays Container Registry Size in usage quotas pages of namespaces and groups.

Related to #356187 (closed)

Screenshots or screen recordings

before	after

How to set up and validate locally

1. Open a Rails console (rails c) and find a namespace to test the feature on (I used "gitlab-instance" group):

   Groups.all # will show you a list of groups, note the id of a particular group
   namespace = Namespace.find(<GROUP_ID>)

2. Enable the container_registry_namespace_statistics feature flag via Rails console

   Feature.enable(:container_registry_namespace_statistics, namespace)

3. Stub container registry statistics via Rails console:

   stats = namespace.build_root_storage_statistics
   stats.container_registry_size = 12_345_678
   stats.save

4. Open local usage quotas page for a group, e.g. http://localhost:3000/groups/gitlab-instance-60b25789/-/usage_quotas#storage-quota-tab

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.