[Tagging] New property Key:walk-in for amenities like clinics, barbers, hair salons that offer walk-in appointments/service?

[Joseph Eisenberg]

Another user has proposed the Key walk-in=* to specify if an amenity,
like a healthcare facility, sees people on a walk-in basis or not. In
particular it's for medical clinics or doctor's practices.

Suggested values are:

yes - walk-in service is available (appointments might also be available)

no - does not normally serve walk-in patients/customers (appointments required).

only - for clinics (or hair salons, barbers, etc) which only provide
"walk-in" service, and do not offer advance appointments

This looks pretty good to me, unless there is a different term used in
British English?

See https://wiki.openstreetmap.org/wiki/Proposed_features/Key:walk-in