Dump per-cpu fields for system when --detail is set (facebookincu…

…bator#10)

For `--detail` and `--everything`, `below dump system...` shows aggregated view over all the CPUs. The change is to show per-CPU details when queried with `--detail` or `--everything` flag.

Before:
```openmetrics
# TYPE system_cpu_softirq_pct gauge
system_cpu_softirq_pct{cpu="-1",hostname="ip-172-31-24-129"} 0 1696365681
# TYPE system_cpu_softirq_pct gauge
system_cpu_softirq_pct{cpu="-1",hostname="ip-172-31-24-129"} 0 1696365685
```

After:
```openmetrics
# TYPE system_cpus_0_softirq_pct gauge
system_cpus_0_softirq_pct{cpu="0",hostname="ip-172-31-24-129"} 0 1696365580
# TYPE system_cpus_1_softirq_pct gauge
system_cpus_1_softirq_pct{cpu="1",hostname="ip-172-31-24-129"} 0.199203187250996 1696365580
# TYPE system_cpus_0_softirq_pct gauge
system_cpus_0_softirq_pct{cpu="0",hostname="ip-172-31-24-129"} 0 1696365585
# TYPE system_cpus_1_softirq_pct gauge
system_cpus_1_softirq_pct{cpu="1",hostname="ip-172-31-24-129"} 0 1696365585
```