Allow excluding services from live services count

Adds a front end for:
https://github.com/alphagov/notifications-api/pull/2417

> Sometimes we have to make a few services for what really is one
> service, for example GOV.UK Pay and GOV.UK Pay Direct Debit. We also
> have our own test services which aren’t included in the count of live
> services. We currently count these as one service by not including
> them in the beta partners spreadsheet.

tests/__init__.py

@@ -178,6 +178,7 @@ def service_json(
         'volume_sms': 222222,
         'volume_letter': 333333,
         'consent_to_research': True,
+        'count_as_live': True,
     }