packit: Run on CentOS stream
packit: Run on CentOS stream

This should allow us to catch test bugs before releases (like the recent
introduction of `dataclass` into testlib, which isn't available in
RHEL/CentOS 8 yet).

Building on CentOS 8 normally only builds the basic packages by
default. Enable optional ones for packit.

garrett/cockpit,mvollmer/cockpit,cockpit-project/cockpit,garrett/cockpit,cockpit-project/cockpit,mvollmer/cockpit,garrett/cockpit,garrett/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,martinpitt/cockpit,mvollmer/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,garrett/cockpit