Add openstack/tempest-horizon in required project
Add openstack/tempest-horizon in required project

Append it in required jobs of vexxhost tenant
Needed-By: https://review.opendev.org/738027

Change-Id: Ie2bd048cf5ced04fd7d98930a3bd75b6dfc91ed8

openstack-infra/project-config,openstack-infra/project-config