Deprecated: use POST /v1/users instead. Sunset: 2026-09-10. Creates a new user in the system. This endpoint allows you to register a new user with their details. The user will be associated with the authenticated client's workspace. The user will still have to create their profile in our Auth0 authentication system, but their data will be linked upon successful login. Email is a mandatory field. Returns the unique identifier of the created user. Save this ID for future actions.