Add basic tests in packit with RHEL

[ekohl]

This is equivalent to https://github.com/theforeman/foreman-installer/pull/921 but uses real RHEL instead of CentOS Stream to test. While CentOS Stream testing is great for visibility to the upstream contributors, CentOS Stream 8 goes EOL in about 2 months. Foreman won't drop EL 8 so aggressively so we may need an alternative. This uses the internal testing farm to run on real RHEL, but has a downside that the results are only visible to Red Hat employees.

It may be possible to mix the two, but this just aims to show how it looks like today.