Add list and kill support for kubernetes CLI

[chadaeschliman]

The metaflow batch CLI supports list and kill for identifying running jobs on a flow and killing them if needed. This is useful if you get disconnected from the terminal that started the job and need to stop it. The kubernetes CLI doesn't have any similar functionality. Our current workaround is to kill the pods manually (and then watch for and kill the retries) which is tedious and error-prone. A much better solution would be to add support for list and kill to the kubernetes CLI.