User info endpoint service

See https://gitlab.hzdr.de/hub-terra/sms/backend/-/issues/77 With this MR here we can query for the current users data in the frontend (currently just the question if active or not).

But this one here is needed in order to know if a user is a superuser later.

Currently this MR only provides the integration fort the backend endpoint - it is not called yet automatically on the login.