Refactor high volume into serialised service model

Just looks a bit tidier and less repetitive.

I’ve only done this for the serialised service because:
- we’re only checking this in places where we’re already using the
  serialised service
- if we want to check this elsewhere there’s a good chance that new code
  should be using the serialised service, since it’ll itself be doing
  some kind of performance optimisation

app/delivery/send_to_providers.py

@@ -87,7 +87,7 @@ def send_sms_to_provider(notification):
             statsd_client.timing("sms.test-key.total-time", delta_seconds)
         else:
             statsd_client.timing("sms.live-key.total-time", delta_seconds)
-            if str(service.id) in current_app.config.get('HIGH_VOLUME_SERVICE'):
+            if service.high_volume:
                 statsd_client.timing("sms.live-key.high-volume.total-time", delta_seconds)
             else:
                 statsd_client.timing("sms.live-key.not-high-volume.total-time", delta_seconds)
@@ -142,7 +142,7 @@ def send_email_to_provider(notification):
             statsd_client.timing("email.test-key.total-time", delta_seconds)
         else:
             statsd_client.timing("email.live-key.total-time", delta_seconds)
-            if str(service.id) in current_app.config.get('HIGH_VOLUME_SERVICE'):
+            if service.high_volume:
                 statsd_client.timing("email.live-key.high-volume.total-time", delta_seconds)
             else:
                 statsd_client.timing("email.live-key.not-high-volume.total-time", delta_seconds)

app/serialised_models.py

@@ -3,6 +3,7 @@ from functools import partial
 from threading import RLock
 
 import cachetools
+from flask import current_app
 from notifications_utils.clients.redis import RequestCache
 from notifications_utils.serialised_model import (
     SerialisedModel,
@@ -106,6 +107,10 @@ class SerialisedService(SerialisedModel):
     def api_keys(self):
         return SerialisedAPIKeyCollection.from_service_id(self.id)
 
+    @property
+    def high_volume(self):
+        return self.id in current_app.config['HIGH_VOLUME_SERVICE']
+
 
 class SerialisedAPIKey(SerialisedModel):
     ALLOWED_PROPERTIES = {

app/v2/notifications/post_notifications.py

@@ -211,7 +211,7 @@ def process_sms_or_email_notification(
         template_with_content=template_with_content
     )
 
-    if service.id in current_app.config.get('HIGH_VOLUME_SERVICE') \
+    if service.high_volume \
         and api_user.key_type == KEY_TYPE_NORMAL \
             and notification_type in [EMAIL_TYPE, SMS_TYPE]:
         # Put service with high volumes of notifications onto a queue