Add memorial=ghost_bike

[Coehill]

https://wiki.openstreetmap.org/wiki/Tag:memorial=ghost_bike

[mnalis]

I'm note sure if those are implemented via id-tagging-schema repository, or via Taginfo popularity, or combination of both (I think it is combination of both).

So I've made a PR at https://github.com/openstreetmap/id-tagging-schema/pull/1302, feel free to review/like there.

[Zverik]

Yup, will appear in 5.2. Thanks for the PR @mnalis !