Desired API addings for SlapOS integration

Those APIs were appended poorly on SlapOS side for a while, but I think registry is mostly the responsable to get those informations (mostly to add some reporting capability).

The main reason is to get some reporting on who is using which IPv6/IPv4 for reporting to an external system (in this case SlapOS) minimal informations about the Re6stnet users.

@jm Could you review and let me know what you think?