block inactive services from making stateful changes

in the NotifyAdminAPIClient, which all api traffic goes through, return
403 for any stateful requests (post, put and delete), if the following
criteria have been met:
* a current_service is set
    (this prevents checks being carried out on non-service related
     updates, eg editing user details)
* the service is not active
* the current user is not a platform admin

so platform admins can still update anything.

Note: Without any specific error handling, the user will see a generic
403 page. This is fine, probably - it's a relatively niche case that
you'll be editing a service you can't get to anyway

app/notify_client/__init__.py

@@ -1,5 +1,5 @@
 from flask_login import current_user
-from flask import has_request_context, request
+from flask import has_request_context, request, abort
 from notifications_python_client.base import BaseAPIClient
 from notifications_python_client.version import __version__
 
@@ -26,3 +26,29 @@ class NotifyAdminAPIClient(BaseAPIClient):
             return headers
         headers['NotifyRequestID'] = request.request_id
         return headers
+
+    def check_inactive_service(self):
+        # this file is imported in app/__init__.py before current_service is initialised, so need to import later
+        # to prevent cyclical imports
+        from app import current_service
+
+        # if the current service is inactive and the user isn't a platform admin, we should block them from making any
+        # stateful modifications to that service
+        print('\n\n\n')
+        print(current_service)
+        print(current_user)
+        if current_service and not current_service['active'] and not current_user.platform_admin:
+            abort(403)
+
+
+    def post(self, *args, **kwargs):
+        self.check_inactive_service()
+        return super().post(*args, **kwargs)
+
+    def put(self, *args, **kwargs):
+        self.check_inactive_service()
+        return super().put(*args, **kwargs)
+
+    def delete(self, *args, **kwargs):
+        self.check_inactive_service()
+        return super().delete(*args, **kwargs)