feat: Collect /sys/net/class PCIE AER counters

[dasturiasArista]

WIP: I would like to get some feedback if this is something that would be accepted. This fully works, but it also has a pending PR in the procfs repo.

Linux provides AER counters in the path /sys/class/net//device/

This is split amoung 3 different files:
aer_dev_correctable
aer_dev_fatal
aer_dev_nonfatal

https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-bus-pci-devices-aer_stats has more information about these counters

I have generated a PR in the proc fs repo as well to keep more in the style of other sysfs collectors.

[dasturiasArista]

prometheus/procfs#686 Has been merged. So would like to merge this simple exporter for that data.