OKD 4.17 introduces a MC override to all config pools that retains the historic default container runtime (runc) for upgrading clusters to OKD 4.18 and above, where the cluster default becomes crun.

This is the relevant code snippet: https://github.com/openshift/machine-config-operator/blob/release-4.17/pkg/controller/container-runtime-config/container_runtime_config_controller.go#L1047-L1123

When upgrading to 4.20, this override should be removed and we should revert to the cluster default of crun. User overrides will still be preserved due to the naming (

> The "00-override" ensures this config is applied between "00-default" and "01-ctrcfg defaultRuntime". This guarantees user-defined ctrcfg settings always override machine-config defaults

Clusters that have been through this migration have a config map created as a marker