It's currently not possible to link a special authorised value category to an ES facet: library, itemtype, location, etc. This is because how (badly) we fetch/cache the authorised values. Improvements must be done in this area before supporting them here.
It's actually branches (homebranch, holdingbranch), itemtype and cn_source. And there is a "special special" that is "language/ln". However some existing hardcoded facets should use the link: Location, Collections. Location is built in _convert_facets (Koha::SearchEngine::Elasticsearch::Search) and Collections in the include file: AuthorisedValues.GetDescriptionByKohaField( kohafield => 'items.ccode', authorised_value => facet.facet_label_value ) Absolutely not consistent!