kubectl deployer defaultNamespace is determined based on current context.

The kubectl deployer's defaultNamespace is determined by the current context's namespace. This behavior only allows applying raw YAML Kubernetes resources with multiple namespaces if the current context’s namespace is set to `default`.

This is unexpected behavior, as the current context's namespace should not affect deploying Kubernetes resources across multiple namespaces. The namespace of the resources should be independent of the current context’s namespace.

Relevant code: https://github.com/GoogleContainerTools/skaffold/blame/b212650a1f0f179aca19b7829332904fe1cb284c/pkg/skaffold/deploy/kubectl/kubectl.go#L93