Add a `node_ethtool_info` metric to all ethtool devices to expose driver
information with following labels:
* bus_info
* driver
* expansion_rom_version
* firmware_version
* version
This metric is useful to monitor the firmware version to be up-to-date.
Note: The version label might be malformed due to bug #39 in ethtool:
https://github.com/safchain/ethtool/issues/39
Signed-off-by: Benjamin Drung <benjamin.drung@ionos.com>