Refactor delete upstream modal component to fetch registries

What does this MR do and why?

Refactor delete upstream modal component to fetch registry names

Update edit upstream component based on refactored component

Changelog: changed

EE: true

Context

1. This feature was initially added in Show associated registries before maven upstrea... (!203775 - merged)
2. We want to reuse this component in other places, like the upstreams list page view.
3. Based on the UX suggestion #576227 (comment 2836370349) we decided

   we can bring in a loader state for the registry names in the modal

4. An MR based on this MR which adds the functionality to the upstreams list page for context: Adds delete upstream action to upstream list view (!211361 - merged)

References

Screenshots or screen recordings

Before	After
Follow screenshots in !203775 (merged)

How to set up and validate locally

1. Go to a group
2. Go to Deploy -> Virtual Registry
3. Create a new maven registry
4. Click on the Add upstream button
5. The required fields are name, url. For the URL, you can use https://repo.maven.apache.org/maven2/
6. Click on Create upstream and observe the list update.
7. Click on the pencil icon for the newly created upstream. This should take you to the edit upstream page.
8. Click on Delete upstream button should show modal with the registry names listed.
9. Create at least 5 more maven registries. Link the same upstream to each of the virtual registry.
10. Clicking on Delete upstream button should show modal with the registry names listed & truncated.

MR acceptance checklist

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Related to #576227