Add intended_date_kwarg field to Schedule (#62)

Co-authored-by: Marc Sabatier <marc.sabatier@eco-adapt.com>

django_q/cluster.py

@@ -691,6 +691,8 @@ def scheduler(broker: Broker = None):
                     if type(args) != tuple:
                         args = (args,)
                 q_options = kwargs.get("q_options", {})
+                if s.intended_date_kwarg:
+                    kwargs[s.intended_date_kwarg] = s.next_run.isoformat()
                 if s.hook:
                     q_options["hook"] = s.hook
                 # set up the next run time