Logging/Monitoring PaSh spawned processes

Currently, it is pretty hard to have any visibility on the dataflow processes that are spawned by PaSh. It would be great if we could have some form of observability of their status/progress.

One way to do it would be to log events related to each of these processes (running, progress (based on INPUT/OUTPUT processed), exit status, etc). Then we could develop a separate extension to analyze and show these logs.

For more info see discussion in #491

Start with the discussion in issue #491, then trace how PaSh spawns its dataflow processes. Define the required events for process status, INPUT/OUTPUT progress, and exit status; done means those events are available for a separate log-analysis extension.

Written by the indexing model from the issue text.