@Alexander, @Rob thanks your time and help, it was a hell of a ride, I really appreciate
it. I think I got pretty solid foundation right now, extended FreeIPA just a little bit,
so I don't expect too much trouble on getting my plugin run on future FreeIPA
releases.
I will have to test it a bit more, but I think, as soon as the checkbox bug is resolved,
I'm good to go.
For the other readers here, I've summed up the process in the readme, the source code
can be found here:
https://github.com/leonidas-o/freeipa-postfixbook-plugin
The container image can be found here:
https://hub.docker.com/r/leonidaso/freeipa-server
Maybe that helps the next one, who is trying to extend FreeIPA or simply wants FreeIPA
already extended with the postfix book schema.