Show associated registries before maven upstream deletion

What does this MR do and why?

Query list of registries associated with upstream added in Adds mavenUpstreamRegistry top-level GraphQL query (!203463 - merged).

Extracts delete upstream logic & modal into a separate modal component which can be reused.

Shows names of associated registries in the modal before maven upstream deletion.

EE: true

References

• Design: #556828[DeleteUpstreamModal.png]
• Move and update delete button style on edit ups... (#565346 - closed)

Screenshots or screen recordings

Description	Before	After
Default
Modal
Modal when registries are associated
Modal when more than 5 registries are associated
When there are no registries associated

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

MR acceptance checklist

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Related to #556828 (closed)