The `linkerd upgrade --from-manifests` command supports reading the
manifest output via `linkerd install`. PR #3167 introduced a tap
APIService object into `linkerd install`, but the manifest-reading code
in fake.go was never updated to support this new object kind.
Update the fake clientset code to support APIService objects.
Fixes#3559
Signed-off-by: Andrew Seigner <siggy@buoyant.io>