fix: secure send_notification endpoint and ensure correct user association

[ObiFaith]

Description

This PR addresses a security issue where the /api/v1/notifications/send endpoint lacks authorization, allowing anyone to send notifications. As a result, the user_id in the notification table is set to NULL, preventing users from retrieving their notifications correctly.
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Related Issue (Link to issue ticket)

• Feat on send_notification
• Fix on send_notification

Motivation and Context

🚀 Security Fix: Ensures that only authenticated users can send notifications.

🔍 Data Consistency: Prevents NULL values in the user_id field.

🛠 User Experience: Ensures that users see the correct notifications associated with their accounts.
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How Has This Been Tested?

The changes have been tested using unit tests and Postman

Screenshots (if appropriate - Postman, etc):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
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Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.