Throw better error when using aggregate functions in versioned queries

src/main/java/org/caosdb/server/query/POV.java

@@ -317,6 +317,10 @@ public class POV implements EntityFilterInterface {
       }
 
       if (getAggregate() != null) { // agg
+        if (query.isVersioned()) {
+          throw new UnsupportedOperationException(
+              "Versioned queries are not supported for aggregate functions like GREATES or SMALLEST in the filters.");
+        }
         callPOV.setString(14, getAggregate());
       } else {
         callPOV.setNull(14, VARCHAR);