services: include Opensearch meta in the results

* Sometimes, keys relevant to the serialization process are not
  included inside ``_source``, i.e. "highlight." By adding
  ``hit.meta`` as part of the serializer context, we make them
  available without the risk of name collision.

Author: egabancho

invenio_communities/communities/services/results.py

@@ -57,6 +57,7 @@ def hits(self):
                 context=dict(
                     identity=self._identity,
                     record=record,
+                    meta=hit.meta,
                 ),
             )
             if self._links_item_tpl: