When running bpftrace programs against a pod, only show the specific pod processes

Right now when you run a bpftrace program against a pod, that is only using the pod to determine the actual binary to use to export symbols by giving you the `$container_pid` variable.

A better pod support would involve having the possibility to filter only pod tasks so that the results are only relevant to the specific pod.

Upstream issue on bpftrace: https://github.com/iovisor/bpftrace/issues/329

Start by reading the upstream bpftrace issue linked in the description and compare its proposed pod-task filtering with the current behavior described here. Done means a bpftrace program run against a pod reports only processes belonging to that specific pod, rather than using the pod only to select the binary for symbol export.

Written by the indexing model from the issue text.