Cannot add custom Kind to Delete Manifest Stage

Issue

When adding the Delete Manifest Stage, Spinnaker will require a Kind field. For the Deploy Manifest Stage, a custom Kind can be added. However, Spinnaker is not able to get the Kubernetes custom Kinds for the Delete Manifest Stage. When trying to add a custom Kind to the Delete Manifest Stage, the user may see an error such as: Exception ( Monitor Delete ) Failed to delete none/ from cluster: error: the server doesn't have a resource type "none"

Cause

The Delete Manifest stage works differently within Spinnaker than the Deploy Manifest stage. The KubernetesDeleteManifestOperatation that is used during the Delete Manifest stage uses the kind's handler to do the deletion. All unregistered kinds use the KubernetesUnregisteredCustomResourceHandler, which always sets the kind to NONE.  This isn't a problem for deploy operations as it doesn't need to do a lookup to find an existing resource, it is just adding the new resource to the cluster. For the delete operations, the current kind needs to be sent as part of the delete operation, but the handler only knows the kind as NONE.