Description of problem:
The OPENSTACK_KEYSTONE_DOMAIN_DROPDOWN and OPENSTACK_KEYSTONE_DOMAIN_CHOICES options were added to Horizon in the OpenStack Pike release. However the keystone_domain_choices puppet parameter which allows setting these options via Director/TripleO was not added to puppet-horizon until the Rocky release.
This should be backported to the Red Hat supported Queens release (OSP13) to align with the Horizon update.
Version-Release number of selected component (if applicable):
Steps to Reproduce:
Upstream THT patch https://review.opendev.org/#/c/715730/ should address this issue. Please note that keystone_domain_choices was added to puppets in RHOSP 14 (Stein), so the change in puppets should also be backported if the goal is to release a fix for RHOSP 13.