It was previously possible to instantiate `Reflector` with
`*unstructured.Unstructured` as the expected type but this did not
support checking that event objects were of the correct API
type (e.g. if event object was `v1.Pod` in `Unstructured` form but
`v1.Service` was expected). This commit adds support for providing a
GVK via an `Unstructured` expected type to compare with the GVK of
event objects. The GVK will also be used in reflector log output.
Kubernetes-commit: 237dbfd8ad322dfcad4bd4d5345368480c22d82f