Add amenity=charging_station to a future version of the schema

[SomeoneElseOSM]

Currently at https://taginfo.openstreetmap.org/keys/amenity#values there are 172k of these worldwide, so it's a frequently used value. Usage is spread fairly evenly across western countries, China and Japan: https://taginfo.openstreetmap.org/tags/amenity=charging_station#map ; It's documented at https://wiki.openstreetmap.org/wiki/Tag%3Aamenity%3Dcharging_station .

It would add value to a general purpose map style that may want to use the Shortbread schema.

It would make sense to add it to wherever amenity=fuel gets added after https://github.com/shortbread-tiles/shortbread-docs/issues/101 (perhaps just "pois", along with car_wash et. al.?)