Update sib:source structure

Today, we have source objects with the following structure:

{
  "@id": "",
  "@type": "ldp:Container",
  "ldp:contains": [
    {
      "federation": "users",
      "container": "https://api.test-nantes.happy-dev.fr/users/",
      "@type": "sib:source",
    },
    {
      "federation": "users",
      "container": "https://api.test-paris.happy-dev.fr/users/",
      "@type": "sib:source",
    }
  ]
}

To support query-ldflex, we need to have an @id property for each resource. Ideally, we would like to get sources like this:

{
  "@id": "",
  "@type": "ldp:Container",
  "ldp:contains": [
    {
      "@id": "https://api.test-nantes.happy-dev.fr/users/",
      "@type": "ldp:Container",
    },
    {
      "@id": "https://api.test-paris.happy-dev.fr/users/",
      "@type": "ldp:Container",
    }
  ]
}