Update pipelines configuration for centos9-stream support

[archanaserver]

#1826

[ekohl]

This PR is not very descriptive. When reading it I don't understand why this is being changed. The summary is also not very helpful.

When I start to look at it, I see the directory also has pipelines/vars/common/foreman_nightly_centos7.yml and pipelines/vars/common/katello_nightly_centos7.yml which makes me wonder: why do we keep those? And further, why do we even have these files? We've supported CentOS 9 for some time and the pipelines were passing.

I have some vague recollection @ehelms used these when manually testing and b62c9d9 (the commit that introduced it) doesn't show any code that actually uses it.

My advice would be to at least also remove CentOS 7 (which is also EOL) and come up with a better summary.

[ehelms]

These are nice to haves, that I use to this day, so that I do not have to remember what all the variables are and what to type out locally, e.g.

ansible-playbook pipelines/install_pipeline.yml -e @pipelines/vars/common/katello_nightly_centos_stream9.yml