Make the default namespace for the command the currently selected namespace for the context

[luis-guimaraes-exoawk]

Hi, in order to better integrate with other Kubernetes tools and the kubectl CLI itself, the rook-ceph plugin should expect the namespace for running commands to be the currently selected namespace in the current Kubernetes context instead of "rook-ceph". This would put it's behaviour in line with kubectl.

This might seem like a nitpick, but these standards help decrease friction in the adoption of new tools :)

Thanks

[subhamkrai]

@luis-guimaraes-exoawk For most cases the namespace is rook-ceph so we defaulted that one but makes sense to check for Kubernetes namespace context.