Add functionality to tail logs via kubectl (or similar tools)

[soenkeliebau]

It would be brilliant to support looking at the logs of our services via kubectl logs

The code to send logs is present and could be used, I have successfully sent "test" messages to kubectl logs, however some extra work needs to be done to read the actual logs from the systemd journal.

I have found two crates that seem to support this functionality, but both have issues if I am not mistaken:

• https://gitlab.com/systemd.rs/sd-journal -> AGPL
• https://github.com/jmesmon/rust-systemd -> unsafe code

I believe this is a medium-low hanging fruit if we can find a crate that offers this functionality, as most of the supporting code could be reused from Krustlet.

[siegfriedweber]

Only the options --follow and --tail are supported. The other options are not forwarded in kubelet.