Added helper to get all S3 objects

A helper function to paginate through a GetObject request to fetch all the objects' `ObjectInfo`.
It pages while `isTruncated` is true.

Unfortunately, the type signature doesn't play well in practice. This is because you can not run it from inside an `aws` monad conventionally. Instead you have to call it with a `ResourceT`.

If you have any ideas how to clean it up, I would be interested. Otherwise, it is very useful anyway.