Show zombie namespaces

[troeger]

Deleting portal users leads to an increasing amount of zombie namespaces, since the portal never removes Kubernetes resources.

In order to compensate for that, there should be some kind of overview in the backend that shows the status of Kubernetes namespaces. This could become part of the K8S namespace list. It would be helpful to have:

• Creation date of the namespace
• Number of running pods
• ...?

Filtering should be flexible, based on these attributes. Superusers can than analyze this list and bulk-delete namespaces accordingly.

[troeger]

See above.