Refactor virtual registries setting component and tests

This is a follow up issue to refactor the virtual registries setting component implementation.

The setup of how the ce group_settings_app component (app/assets/javascripts/packages_and_registries/settings/group/components/group_settings_app.vue) and ee virtual registries setting component work together can be improved. This will help when we need to expand the settings to include other settings and also will help with maintaining tests so there is no duplication.

The options are noted here in this discussion on the original MR.

Reference: !203628 (comment 2815639245)

Example of a similar setups:

!192417 (diffs) !195824 (merged)

• Refactor the component and tests
• Fix up the capitalization on the header for virtual registry and also the dependency proxy.