Validate sign up against existing users

Summary Instead of allowing all requests if entered correctly, Directus should check if a User already exists with the same email address. Basic Example Sign up with: { "email": "[email protected]", "password": "Start123!", "first_name": "test", "last_name": "user" } Response 204 No Content But if another User signs up with: { "email": "[email protected]", "password": "Start123!", "first_name": "user", "last_name": "test" } Still response 204 No Content even though someone already registered with the same email Motivation It improves API usability and removes reduntant workarounds. Detailed Design When a user is already registered with an email, directus should respond with something like 409 Conflict - User already registered. It can also be something more inconspicuous…