[Platform] [User Notifications][TUS] Notifications are generated asynchronously after event is created

[becevka]

Summary
In order to support User Notifications, we need to generate them for the subscribed users after event was created.

Describe the solution you'd like
Notifications Collection should consist of the following fields:

• event, reference to Event Collection
• user, reference to the user subscribed to Business Entity
• createdDateTime, date when event was created
• readDateTime, date when event was marked as read and switched to be inactive

When Event is created, async routine is invoked to generate Notifications as follows:

• based on event.entityId and event.entityType, select all users from Subscription Collection with 'active' subscriptions.
• for each user, create new Notification pointing to new event and selected user, keep readDateTime as null.

Acceptance Criteria

Generated by Zenhub AI

• Scenario: Notifications are generated asynchronously after event creation
  • Given an event is created
  • When the event is created
  • Then an async routine should be invoked to generate notifications for subscribed users
• Scenario: Notifications Collection
  • Given a Notifications Collection exists
  • When a new notification is generated
  • Then the Notifications Collection should contain the following fields:
    • event, reference to Event Collection
    • user, reference to the user subscribed to Business Entity
    • createdDateTime, date when event was created
    • readDateTime, date when event was marked as read and switched to be inactive