KEYCLOAK-4593 Flush and clear when fetching multiple realms for performance improvement with large number of realms

model/jpa/src/main/java/org/keycloak/models/jpa/JpaRealmProvider.java

@@ -117,7 +117,8 @@ public class JpaRealmProvider implements RealmProvider {
         for (String id : entities) {
             RealmModel realm = session.realms().getRealm(id);
             if (realm != null) realms.add(realm);
-
+            em.flush();
+            em.clear();
         }
         return realms;
     }