Throttle email notifications upon updating document frequently (#4026)

* feat: add needed columns for throttling notifs

* feat: update model

* feat: deliver only one notif in a 12 hour window

* fix: address review comments

* prevent retry if notification update fails
* fix type compatibility instead of circumventing it
* add index for emailedAt

* fix: add metadata attr to EmailProps

* chore: decouple metadata from EmailProps

* chore: add test

* chore: revert sending metadata in props

server/types.ts

@@ -305,3 +305,7 @@ export type Event =
   | UserEvent
   | ViewEvent
   | WebhookSubscriptionEvent;
+
+export type NotificationMetadata = {
+  notificationId?: string;
+};