feat(server): support read all notifications (#13083)

close AF-2719



#### PR Dependency Tree


* **PR #13083** 👈

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **New Features**
* Added the ability to mark all notifications as read with a single
action.
  
* **Bug Fixes**
  * Ensured notifications marked as read are no longer shown as unread.

* **Tests**
* Introduced new tests to verify the functionality of marking all
notifications as read.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/schema.gql

@@ -1236,6 +1236,9 @@ type Mutation {
   """queue workspace doc embedding"""
   queueWorkspaceEmbedding(docId: [String!]!, workspaceId: String!): Boolean!
 
+  """mark all notifications as read"""
+  readAllNotifications: Boolean!
+
   """mark notification as read"""
   readNotification(id: String!): Boolean!
   recoverDoc(guid: String!, timestamp: DateTime!, workspaceId: String!): DateTime!