support dynamic kubelet config

[cjroebuck]

https://kubernetes.io/docs/tasks/administer-cluster/reconfigure-kubelet/

i.e. set the --dynamic-config-dir flag of the kubelet so users can amend the kubelet config.

Would allow the user to configure things like the max eviction grace period #19 which is currently being set to 0.

[timoreimann]

I can see how more flexibility in customizing certain kubelet parameters (and control plane parameters as well, for that matter) can be useful to users.

One thing we have to watch out for as managed service owners is complexity in the offered configuration space: opening up kubelet parameters in a generic way means lots of flexibility for customers but also lots of opportunities to shoot yourself in the foot or potentially break existing work flows that we support (like cluster version upgrades).

A safer approach could be to look at individual configuration parameters that users are asking to make tweakable (like the eviction grace period) and evaluate on a case by case basis how we can support those.