feat: send notification as email digest implementation

[CFCIfe]

Add Email Digest Implementation for Notifications

Description

This pull request adds the implementation for sending notifications as email digests. It includes the following changes:

• Ability to send 2 emails from all user notifications to them by 8 P.M

Changes Made

• Notification:

  • Extended the notification entity to include created_by field.

• NotificationsModule:

  • Integrated services and logic to support the generation and sending of email digests.
  • Added schedulers to handle the dispatching of email digests based on user preferences.

• package.json:

  • Updated dependencies to include any new packages required for email digest functionality (e.g., email sending libraries).

How to Test

1. Setup:

   • Ensure your environment is configured with the necessary email service credentials.
   • Run npm install to update dependencies.

2. Testing Email Digest Creation:

   • Create a notification and check if it's correctly marked for inclusion in an email digest.

3. Testing Email Sending:

   • Ensure the scheduler triggers and sends an email digest at the specified intervals.
   • Verify that the email content includes all the notifications marked for the digest.

4. Testing User Preferences:

   • Update user notification settings to include preferences for email digests.
   • Check that the system respects these preferences when creating and sending email digests.

Authentication Errors

• If the user is not authenticated, the system should prevent access to notification creation and retrieval endpoints.
• Verify that proper error messages are returned for unauthenticated access attempts.

Invalid User ID Errors

• The system should validate user IDs before creating or sending notifications.
• Ensure that errors are handled gracefully, and informative messages are provided.

Validation Errors

• Ensure all notification-related DTOs are validated correctly.
• Test for missing or incorrect fields and check that appropriate error messages are returned.

Additional Notes

• This implementation assumes that the email service is configured and operational.
• Future improvements may include more customizable digest templates as well as plugging the notification system into other services.

Checklist

• I have performed a self-review of my code.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• New and existing unit tests pass locally with my changes.