Initialise clients outside the app

This avoids the annoying problem where you can’t import a client unless
the app has already been initialised.

app/notify_client/organisations_api_client.py

@@ -52,3 +52,6 @@ class OrganisationsClient(NotifyAdminAPIClient):
             url="/organisations/unique",
             params={"org_id": org_id, "name": name}
         )["result"]
+
+
+organisations_client = OrganisationsClient()