Register a before_request event for all blueprints, that defines the authentication requirement.

There are three authentication methods:
 - requires_no_auth - public endpoint that does not require an Authorisation header
 - requires_auth - public endpoints that need an API key in the Authorisation header
 - requires_admin_auth - private endpoint that requires an Authorisation header which contains the API key for the defined as the client admin user

tests/app/notifications/test_process_client_response.py

@@ -1,6 +1,5 @@
 import uuid
 
-from app.models import NotificationStatistics
 from app.notifications.process_client_response import (
     validate_callback_data,
     process_sms_client_response