We need to test and adjust routing for internal and external federation.

• UA enforcement to be considered for external only, meaning requests from query-next and query-scholarly-next should not be UA-gated.
• Verify the possibility to enforce/change the UA on Qlever federation requests.

Test query (TODO: better test query with less results which make it obvious that federation actually works):

SELECT ?item ?bhl_id WHERE {
  { 
    ?item wdt:P4327 ?bhl_id . 
  }
  UNION
  {
    SERVICE <http://query-scholarly-next.wikidata.org/sparql> {
      ?item wdt:P4327 ?bhl_id . 
    } 
  }
}

AC

• query-external and query-scholarly-external public endpoints can federate with each other