Add Tempest gate job for stable/wallaby

Now we have stable/wallaby branch ready for devstack
and so does for all service projects.

This commit adds the Tempest testing for stable/wallaby
by adding new jobs running on stable/wallaby version of
openstack.

Depends-On: https://review.opendev.org/c/openstack/devstack/+/784974
Change-Id: Ibb69384be54e284d59950371238a64c041348000
2 files changed