Get details of container virtual registry upstream

Proposal

We add a query to get the details of a container virtual registry upstream given a upstream ID.

query {
  virtualRegistriesContainerUpstream(id: "gid://gitlab/VirtualRegistries::Container::Upstream/5"){
    id
    description
    name
    registryUpstreams {
      id
      registry {
        name
      }
    }
  }
}