Feature: add support for calico

[deggja]

Currently, the implementation fetches policies from namespaces, and some logic is based on there being a namespace field in the structure of the kubernetes resource.

At some point it would be nice to add support for global network policies from e.g Calico and others. These policies do not have a namespace field and wont be included currently.

type PolicyVisualization struct {
	Name       string   `json:"name"`
	Namespace  string   `json:"namespace"`
	TargetPods []string `json:"targetPods"`
}