get https://www.sefaria.org/api/category/
GET requests take a full category path in the request, e.g. /api/category/Tanakh/Torah/Genesis, and return the full category object found.
If the category is not found, the returned object will have an error attribute. If any element of the path is found, the API will return the closest parent in an attribute called closest_parent. This is useful for proactively looking up a category before posting an Index to it.