[Feature Request] Add ageRating field on metadata

[TimilsinaBimal]

Currently stremio doesn't use ageRating on it's metadata. While there are ways we can manage it be it by streams or concatenating with imdbRating or any other fields, it would be better if this will be supported natively. So, addon provides ageRating field in meta or catalog request and it will be displayed along with imdbRating in movie/series listing.