[jormun]: add parameter requested_datetime in direct_path journey

Attribute journey.requested_date_time is absent in direct_path journey provided by some connectors like Andyamo and Geovelo.
Even if this information is deprecated since some years (https://github.com/hove-io/navitia/blob/c7ab2702ad8cfa6e22e8427cd6fca3b4cdbe6ff7/source/jormungandr/jormungandr/interfaces/v1/serializer/journey.py#L435), attribute is added for these two connectors.
Attribute is present for connectors like Asgard, RideSharing, and others..

hove-io / navitia