Add network monitoring for kubernetes pods and when run as container

[phip123]

The feature should basically act the same way as it already exists for docker containers (docker_cgrp_net).

The instrument's name should be kubernetes_cgrp_net to keep a consistent naming scheme.

[phip123]

This will probably not work as currently the docker_cgrp_net instrument does not work when running as a container due to the currently used alpine base image.

[phip123]

This issue now covers the new instrument (kubernetes_cgrp_net) as well as an implementation that supports native execution and container use.