Fixes https://github.com/dhall-lang/dhall-kubernetes/issues/86
The motivation of this is to more accurately model the Kubernetes
API semantics by not auto-omitting empty fields. This is because
a field set to `Some ([] : List T)` is not necessarily the same
as `None (List T)`.
This makes the typical case a bit more verbose (more `Some`s), but
the difference to the `./examples` shows that it's not too bad.
This improves the granularity of the Nix build graph in order to minimize
unnecessary rebuilds.
This also fixed several bugs in the package generation along the way, so
this change includes those fixes.
