Add sort to Single Document Response

[tallnato]

we need to have the sort field so we can use for pagination with the search_after property

[0xTim]

Thanks for suggesting this! I'm not overly comfortable taking AnyCodable here primarily because it doesn't have a stable API to rely on. It also starts to get really difficult when we need to make things Sendable. A better approach would probably be with generics to allow a user to pass in the search document as a generic Codable type, similar to how Document works in ESGetSingleDocumentResponse.

The PR will also need tests