Export CPU cores metrics

[mr-karan]

Was going through the 1.73.0 Release Notes and came across this issue where process_cpu_cores_available which is available in all Victoriametrics components.

I am wondering, shouldn't this be available inside metrics library as well over here: https://github.com/VictoriaMetrics/metrics/blob/master/process_metrics_linux.go

This library already exports process specific CPU/Memory/IO metrics, so might be a good place to add it here so all users of this library can get access to process_cpu_cores_available as well?

Thanks