When recursively diffing Kustomization objects on a cluster, each
Kustomization is built and then a server-side dry-run apply is
performed. This isn't practical to perform if the Kustomization
references a remote cluster via `kubeConfig.secretRef`.
Currently, because it's not skipped, it's treated as though it's
being applied to the context cluster, not the remote cluter, which
results in an incorrect diff.
Instead, write out special message / warnings indicating that it
has been skipped:
```
► Kustomization/my-ns/my-kst skipped: diff not supported for remote clusters
```
Signed-off-by: Milas Bowman <devnull@milas.dev>
7697699e65