Support finding unused namespaces

[liornoy]

Add a new "namespace" command to find unused namespaces.

This command determines whether there are any used resources
within a given namespace, if there are no used resources,
the namespace is considered unused.

fixes #92

[yonahd]

Hi @liornoy
This is a good direction but this would miss some resources that may be present such a jobs, cron jobs or any other resource kor doesn't track.

[luisdavim]

Hi @liornoy This is a good direction but this would miss some resources that may be present such a jobs, cron jobs or any other resource kor doesn't track.

Yeah, this may lead to many false positives, one approach could be to get a list of resource types from the user and check if any of those exist in the given namespace, or get a list of namespaced resource types from the API and use that to check the NS. Something like what this plugin does https://github.com/corneliusweig/ketall/tree/master

We also have to take into account the default resources in a namespace, like the default service account and its secret for example.

[liornoy]

Thanks for the review @yonahd @luisdavim !
I'll take a look into this ketall tool and rethink my approach here.

[yonahd]

@liornoy Do you intend to retry this MR or should I have someone else attempt it?

[liornoy]

@yonahd Hi! please do un-assign me. I can't seem to make this work in the time that I have.

[yonahd]

Thanks for the attempt!
Hope to see you back here in the future