Add table headers for maven virtual registries list view

What does this MR do and why?

Add table headers for maven virtual registries list view

Adds default empty illustration for empty state.

EE: true

Changelog: changed

References

• Design: #556837[MavenRegistriesList.png]
• We've decided not to add the maven icon for each row.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Visit /groups/<group-name>/-/virtual_registries/maven
2. Confirm empty state illustration update.
3. Create registry.
4. Re-visit /groups/<group-name>/-/virtual_registries/maven.
5. Confirm table view, links to edit & show registry work as expected.
6. Log in as guest and confirm that edit link is not visible.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #576229 (closed)