Add probe for Kubernetes ingress

[bzurkowski]

Add Kubernetes probe for Ingress resource. Ingress elements should be linked to services.

Python client method: list_namespaced_ingress (see all methods)

In order to add a new probe, one need to implement probe and linker. The former pulls upstream entities (i.e. K8S objects) and inserts them into entity graph. The latter links inserted graph nodes. In other words: probes create graph nodes, whereas linkers create graph edges.

Below, an example implementation of related modules for K8S Service object:

• probe - provisions a probe instance
• extractor - extracts node element from raw upstream entity
• linker - provisions a linker instance
• matcher - matches two nodes based on matching condition, used by linker
• init - provisions a probe bundle (probe + linkers)