powersupplyclass metrics have missing and non-base units

I was researching for a blog post, and noticed some issues with the metrics from the powersupplyclass collector.

Only a few of the metrics have units, e.g. node_power_supply_current_ampere has a unit but many including node_power_supply_current_max are missing units.
There's also some units that appear to be incorrect and/or not base units. My laptop doesn't have the metric so I can't be sure, but the unit on node_power_supply_charge_ampere looks to be wrong as it's actually Ah per the kernel docs (https://www.kernel.org/doc/Documentation/power/power_supply_class.txt) - which should be exposed as columbs (i.e. amp seconds). For node_power_supply_energy_watthour should be using the base unit of joules. The capacity metrics are percentages, so should be converted to ratios.

Several labels of node_power_supply_info seem to be able to change over time, including at least capacity_level, status, charge_type and health so should probably be split out into an enum similar.

The powersupplyclass collector is the entry point; compare its exported metrics and values with the kernel power_supply_class documentation. Done means relevant metrics use correct base units or ratios, and changing status-like values are represented as an enum rather than labels.