Update ft_billing DAO functions to use postage

* Updated the 'fetch_billing_data_for_day' DAO function to take postage into
account
* Updated the 'update_fact_billing' DAO function to insert postage for
new rows. When updating rows which are identical apart from the postage, the
original row will be kept. (This behaviour will change once postage is
added to the primary key - at this point, upserting will add a new row.)
* Also changed some fixtures / test set up functions to take postage
into account

app/dao/fact_billing_dao.py

@@ -169,6 +169,7 @@ def fetch_billing_data_for_day(process_day, service_id=None):
         func.sum(table.billable_units).label('billable_units'),
         func.count().label('notifications_sent'),
         Service.crown,
+        func.coalesce(table.postage, 'none').label('postage')
     ).filter(
         table.status.in_(NOTIFICATION_STATUS_TYPES_BILLABLE),
         table.key_type != KEY_TYPE_TEST,
@@ -182,7 +183,8 @@ def fetch_billing_data_for_day(process_day, service_id=None):
         'letter_page_count',
         table.rate_multiplier,
         table.international,
-        Service.crown
+        Service.crown,
+        table.postage,
     ).join(
         Service
     )
@@ -254,7 +256,8 @@ def update_fact_billing(data, process_day):
         international=billing_record.international,
         billable_units=billing_record.billable_units,
         notifications_sent=billing_record.notifications_sent,
-        rate=billing_record.rate
+        rate=billing_record.rate,
+        postage=billing_record.postage,
     )
 
     stmt = stmt.on_conflict_do_update(
@@ -279,6 +282,7 @@ def create_billing_record(data, rate, process_day):
         international=data.international,
         billable_units=data.billable_units,
         notifications_sent=data.notifications_sent,
-        rate=rate
+        rate=rate,
+        postage=data.postage,
     )
     return billing_record