Add trial_from_plan, trial_period_days args to Customer.subscribe()

Closes dj-stripe#709

djstripe/models.py

@@ -883,7 +883,8 @@ def pending_charges(self):
 
     def subscribe(
         self, plan, charge_immediately=True, application_fee_percent=None, coupon=None,
-        quantity=None, metadata=None, tax_percent=None, trial_end=None
+        quantity=None, metadata=None, tax_percent=None, trial_end=None, trial_from_plan=None,
+        trial_period_days=None
     ):
         """
         Subscribes this customer to a plan.
@@ -922,6 +923,14 @@ def subscribe(
         :param charge_immediately: Whether or not to charge for the subscription upon creation. If False, an
                                    invoice will be created at the end of this period.
         :type charge_immediately: boolean
+        :param trial_from_plan: Indicates if a plan’s trial_period_days should be applied to the subscription.
+                                Setting trial_end per subscription is preferred, and this defaults to false.
+                                Setting this flag to true together with trial_end is not allowed.
+        :type trial_from_plan: boolean
+        :param trial_period_days: Integer representing the number of trial period days before the customer is
+                                  charged for the first time. This will always overwrite any trials that might
+                                  apply via a subscribed plan.
+        :type trial_period_days: integer
 
         .. Notes:
         .. ``charge_immediately`` is only available on ``Customer.subscribe()``
@@ -942,6 +951,8 @@ def subscribe(
             metadata=metadata,
             tax_percent=tax_percent,
             trial_end=trial_end,
+            trial_from_plan=trial_from_plan,
+            trial_period_days=trial_period_days,
         )
 
         if charge_immediately: