The payload when receiving a notification webhook is pointless without
knowing which user the notification is for. This fix adds the user_id to
the notification serializer so that when you receive a notification
webhook you can properly identify which user the notification is for.
See
https://meta.discourse.org/t/getting-the-target-user-for-notification-webhook-events/129052?u=blake
for more details.
Blake Erickson