Add registry setup instruction for group level endpoint

🍀 Context

In #299834 (closed) we're adding support for group level endpoints for npm Registry

🔥 Problem

There is a registry setup step on the package's details page. We need to add a group level endpoint instruction in there.

🚒 Solution

Add a new radio button "Group-level" with the correct group level endpoint. For that we need:

backend

• Add a new field that returns group-level url to the PackageDetailsType https://docs.gitlab.com/ee/api/graphql/reference/#packagedetailstype

frontend

• Modify npm_installation component to add new option to packageEndpointTypeOptions
• use the new field proposed in backend to render the instruction