The image definition is shared with the latest RHEL 8.y one (8.4 currently).
I expect that we the introduction of 8.5 support, we point the centos 8
distro at it.
The test repositories and manifests use the official CentOS composes. From
what I can tell, they are persistent. This is not guaranteed though, so we
might need to switch to RPMRepo at some point.
The "classic" CentOS 8 should also be buildable but due to the chicken and egg
issue (this commit will get into Centos "8.4" but Centos "8.4" isn't a thing
yet), we cannot test it and therefore it might be broken.
Signed-off-by: Ondřej Budai <ondrej@budai.cz>
