Match on partial email addresses in search

Users expect the search to work on partial email addresses ‘similar to
Gov.Pay’. We can’t have a situation where Pay are doing something better
than us 😜

app/dao/notifications_dao.py

@@ -446,7 +446,7 @@ def dao_get_notifications_by_to_field(service_id, search_term, statuses=None):
 
     filters = [
         Notification.service_id == service_id,
-        Notification.normalised_to == normalised,
+        Notification.normalised_to.like("%{}%".format(normalised)),
         Notification.key_type != KEY_TYPE_TEST,
     ]