cai_scale field should not lowercase its value

[lucadelu]

There is a problem if a user try to add cai_scale tag manually, the value should be uppercase but it convert automatically lowercase. It seems similar to openstreetmap/iD#8609 and openstreetmap/iD#8275.

[tyrasd]

It was actually a bit more similar to openstreetmap/iD#3377. But let's add a country-specific field for hiking routes to the tagging schema as well (:arrow_right: #293).