Adds Role-based functionality

[Sammuel09]

What does this PR do?

• Adds Role-based functionality to the App. That is, a super admin can assign users to be an admin.

Description of Task to be completed?

• Create Role-based functionality.
• Set up tests.

How should this be manually tested?

• Use git fetch to clone this branch.
• Switch to this branch in your machine.
• Run npm run dev to start the server.
• Using postman, send a put request to http://localhost:3000/api/v1/users/<usernameofverifieduser>
• If you do not have a verified user in your DB, create one by signing up.
• This request should be sent with a superAdminToken as a bearer.
• You get a response in format:

{ "status": "success",
    "data": {
        "statusCode": 200,
        "message": "The User role has been upgraded to Admin",
        "error": null,
        "payload": {
            
        }
    }
}

• You can test this feature by running npm t

What are the relevant pivotal tracker stories?

Link to Pivotal Tracker Story

[tejiri4]

LGTM, yet.

[rafmme]

LGTM, yet

[ebzeal]

LGTM yet