feat(setup) Sizelimit error instead of HTTP timeout for PHP<7.3

If we cannot paginate and there are too much entries, bail out.

issue #2895

setup/class_setupStepMigrate.inc

@@ -1031,6 +1031,7 @@ class setupStepMigrate extends setupStep
         }
       } else {
         /* fallback to search without pagination */
+        $ldap->set_size_limit(static::$objectNumberLimit);
         $res = $ldap->search($filter, ['dn']);
         if (!$res) {
           throw new CheckFailedException(
@@ -1038,6 +1039,12 @@ class setupStepMigrate extends setupStep
             _('Possibly the "root object" is missing.')
           );
         }
+        if ($ldap->hitSizeLimit()) {
+          throw new CheckFailedException(
+            _('Sizelimit hit'),
+            sprintf(_('Sizelimit of %d hit. Please check this manually'), static::$objectNumberLimit)
+          );
+        }
       }
 
       while ($attrs = $ldap->fetch()) {