/user/<user_id> -- Promoting the user to Admin

[varun10sudhir]

A route to promote the user to admin
A request header by the name 'admin_code" needs to be present with a password that will promote a user to admin access
Assume the pasword is "admin"
If the correct password is inputted, promote the user to Admin and return an appropriate JSON message
If the password is incorrect , return a JSON message informing the user that he has been denied access