Description of problem:
An external trust is a trust relationship between Active Directory domains that
are in different Active Directory forests. While forest trust always requires
to establish trust between root domains of the Active Directory forests,
external trust can be established to any domain within the forest.

User Story:
As an Active Directory Administrator, I want to establish trust between IdM
Server and my domain only. The trust between IdM Server and an external Active
Directory domain will be non-transitive as no users or groups from other Active
Directory domains will have access to IPA resources.