[Fixes #14134] Migrate userinfo endpoint to DRF

[nrjadkry]

Fixes #14134

The new endpoint is /api/v2/userinfo/

The error response format for unauthenticated requests has been updated to follow standard procedure. Here is the example of the response in case of unauthenticated user

Previous:

{
    "success": false,
    "status": "error",
    "errors": {
        "user": [
            "User is not authenticated"
        ]
    }
}

Current:

{
  "success": false,
  "errors": [
    "Authentication credentials were not provided."
  ],
  "code": "not_authenticated"
} 

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[gemini-code-assist]

Code Review

This pull request refactors the user_info endpoint from a function-based view to a Django Rest Framework class-based view (UserInfoView). While the transition to DRF improves the code structure, the original implementation's CSRF exemption was omitted in the new class-based view. Feedback suggests restoring this exemption using @method_decorator(csrf_exempt, name='dispatch') to maintain compatibility with existing clients and ensure functional parity with the previous implementation.