Capture procs_running threads with metricbeat

[111andre111]

Describe the enhancement:
As of today there is no possibility to have insight to metricbeat processes from a thread based perspective

Describe a specific use case for the enhancement or feature:
The idea is to enrich procs_running as numbers of threads to the system.summary metricset.
Possibly with a having a special section process.summary in order to clarify the concept to the other metrics.
https://www.elastic.co/guide/en/beats/metricbeat/current/metricbeat-module-system.html#_process_summary
Normally these ones are avalable under procs_running metric in stat file:
cat /proc/stat | grep procs_running
https://www.linuxhowtos.org/System/procstat.htm

The running field contains only the numbers of processes on the given system:
https://www.elastic.co/guide/en/beats/metricbeat/current/exported-fields-system.html#_process_summary_2

Thanks a lot.

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)