[feature request] support Intel CPU Uncore Frequency

Uncore Frequency plays an important role in AI workloads.
It hurts performance badly if the frequency is low.
We'd like to monitor min_freq_khz, max_freq_khz and current_freq_khz.

1. monitor min_freq_khz and max_freq_khz to check if the bios configuration is correct:

# cat /sys/devices/system/cpu/intel_uncore_frequency/uncore00/{min_freq_khz,max_freq_khz}
2200000
2200000

2. monitor current_freq_khz to check if there is a electrical power issue:

# cat /sys/devices/system/cpu/intel_uncore_frequency/uncore00/current_freq_khz
2200000

Start by locating the node_exporter collector that reads Linux CPU sysfs data, then inspect the Intel uncore paths under /sys/devices/system/cpu/intel_uncore_frequency/uncore00/. Add monitoring for min_freq_khz, max_freq_khz, and current_freq_khz, and verify that the exported metrics reflect the sample values shown in the issue.