Document the non-zero exit code that is displayed after RKE2 processes

[caroline-suse-rancher]

Some of our customers and users have expressed interest in having the RKE2 exit behavior better documented. The exit code is non-zero, which some have argued is confusing and unclear. The ask here is for this behavior to be explained in an accessible and public area within our RKE2 documentation.

[brandond]

There are a bunch of controllers that trigger a fatal exit when the context is cancelled by the process receiving a shutdown signal. This results in the process exiting with a non-zero return code. It hasn’t been a priority to find and resolve all of the places where this occurs (many of them being in wrangler or core Kubernetes) as the issue is purely cosmetic in that systemctl status shows failed instead of exited when the service is stopped. Systemd also does not like that the container processes remain running after the main rke2 process exits, but that is a separate issue.