Add support to with for nested Optional record merge

[TristanCacqueray]

This issue capture the results of this thread

In short, would it be possible to support this use-case:

let Kubernetes = ./package.dhall

let x =
      Kubernetes.DeploymentSpec::{
      , template = Kubernetes.PodTemplateSpec::{
        , metadata = Kubernetes.ObjectMeta::{ name = "test" }
        , spec = Some Kubernetes.PodSpec::{ hostname = Some "host" }
        }
      }

in    x with { template.spec.serviceAccount = Some "builder" }
    : Kubernetes.DeploymentSpec.Type