fix encoding of time property

needs to be an object as of
https://docs.ogc.org/DRAFTS/20-004.html#_overview_4

pygeoapi/provider/csw_facade_dcat.py

@@ -266,7 +266,7 @@ def _owslibrecord2record(self, record):
             'id': record.identifier,
             'type': 'Feature',
             'geometry': None,
-            'time': record.date or None,
+            'time': {"timestamp": record.date} if record.date is not None else None,
             'properties': {},
             'links': [
                 self._gen_getrecordbyid_link(record.identifier),