Provide a 'list' command

[xakraz]

First of all, thanks for your time and for open-sourcing this tool. It is nice to have something handy like that which ease daily usage of Kube resources.

From a UX point a view, it would be even nicer to have a list command.

It could just a wrapper for kubectl get cronjobs.batch command. It feel very needed while using this kubectl plugin

kubectl cron **list**
kubectl cron run
kubectl cron suspend
kubectl cron unsuspend