In order to promote kubectl alpha events to beta,
it should at least support flags which is already
supported by kubectl get events as well as new flags.
This PR adds;
--output: json|yaml support and does essential refactorings to
integrate other printing options easier in the future.
--no-headers: kubectl get events can hide headers when this flag is set for default printing.
Adds this ability to hide headers also for kubectl alpha events.
This flag has no effect when output is json or yaml for both commands.
--types: This will be used to filter certain events to be printed and
discard others(default behavior is same with --event=Normal,Warning).
