Update default "Centos" environment to 8

[aztechian]

I'm not 100% sure this is the right action, but definitely CentOS 7 is EOL and gone.

Whether this is a fork of RHEL currently (is there one... Fedora, Alma?)

Ask @gregshep for guidance here on what would be most helpful to see.
I'm also going to create a new issue for adding a Debian environment and worker.

[gregshep]

I think Rocky Linux 8 or better might be Rocky Linux 9. These are the best successors to CentOS in my estimate :-)