implement "validate" command to validate manifest againest specifc type schema

[murali-reddy]

Little farfetched idea for kube-shell. Though doable with python jsonschema question is does it fit to context/themes/use-cases of kube-shell.

kube-shell> validate nginx-pod.yaml should throw out manifest errors if any.

[murali-reddy]

Will re-open if it make sense later. closing it for now.