[FEAT-REQ] Add support for available countries

[kanytu]

Some apps are only available in some counties

Would it be possible to add support to fetch those available countries?

I'm unsure if the nodeJS has that feature too.

[JoMingyu]

I don't know if it's technically easy, but I'll try.

[pnu-s]

Something which may be easier would be to get whether the app is available in the country you specified in the country option