Add highway=services to a future version of the schema

[SomeoneElseOSM]

Currently at https://taginfo.openstreetmap.org/keys/highway#values there are 30k of these worldwide, so it's a frequently used value. Usage is spread evenly across the world; it's not a value that is used more commonly by some OSM communities to express that concept than others. It's documented at https://wiki.openstreetmap.org/wiki/Tag%3Ahighway%3Dservices.

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 one of https://shortbread-tiles.org/schema/1.1/#land-use-land-cover-buildings

perhaps https://shortbread-tiles.org/schema/1.1/#layer-sites ("This layer is for types of land use that will usually be above the basic land layer, but below buildings.")

or if not that, just https://shortbread-tiles.org/schema/1.1/#layer-land