UX updates to maven registries list & edit pages

What does this MR do and why?

UX updates to maven registries list & edit pages

Update the cancel button logic in the edit registry form to redirect to the registry detail page instead of the list page.

Implement logic to hide the Create registry button when a top-level group has 20 or more Maven virtual registries.

EE: true

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Ensure you have enabled the following feature flags

$ gdk rails console
Feature.enable(:maven_virtual_registry)
Feature.enable(:ui_for_virtual_registries)

2. Then run the following to create 20 Maven registries

g = Group.find(<group-id>)
20.times.each { |i|  VirtualRegistries::Packages::Maven::Registry.create(group: g, name: "maven registry - #{i}") }

2. Go to top-level group
3. Go to Deploy -> Virtual Registry, then click on Maven
4. With the changes in this MR confirm that Create registry button is not visible for maintainer+ users
5. Click on the edit icon should load the Edit registry page.
6. confirm that clicking cancel button takes you to registry detail page & not the registries list page.
7. Delete a registry from the Edit registry page.
8. Confirm that Create registry button is now visible

MR acceptance checklist

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Related to #569351 (closed)