[docs] Clarify the downsides of missing `systemd` integration in `Podman`

[tobwen]

summary

I noticed that the documentation mentions the lack of systemd integration. I guess it would be helpful to tell the users about the consequences of that. Highlighting these types of real-world effects would help users better understand the trade-offs and make informed decisions.

examples

For example, some concrete impacts of missing systemd integration might include...

• Logging issues: Without systemd integration, conmon's logs aren’t easily directed to the system journal, making troubleshooting more difficult in systemd-based environments.

• kubelet instability: When running Kubernetes, if the node is using cgroupfs instead of systemd, and kubelet is started assuming systemd cgroups, it can lead to node instability and crashes over time. Users need to explicitly configure kubelet for cgroupfs and possibly avoid systemd as the init system in such cases.

[kosovojs]

not 100% sure if that's the reason (would love to have confirmation), but missing systemd also means that healthchecks don't work - if you configure healtchecks, they don't execute and container is in "starting" phase.