fix: internal server error

[daviduzondu]

What does this PR do?

This PR issues a fix on /api/v1/users/export that throws an internal server error when the user request for his data.

How should this be manually tested?

Send a GET request to this endpoint:

GET /api/v1/users/export

Request Headers:

{
   "Authorization": "Bearer <token>"
}

Error Responses:

• Error Response (400):

{
  "message": "Admin Role does not exist",
  "status_code": 400
}

• Error Response (401):

{
  "message": "User is currently unauthorized, kindly authenticate to continue",
  "status_code": 401
}

Checklist of what you did

• Improve the code in the User Service to exclude relations with no join column
• Write unit tests to make sure that everything works.

Test Screenshot

Reference Issue

#138