🐛 Preserve unstructured object GVKs in cache.Options.ByObject

[joelanford]

This patch enables unstructured objects that have populated GVKs to be used as keys when configuring ByObject cache options.

Prior to this patch, a cache setup like the following causes manager.New to return an error with "unstructured object has no kind":

obj := &unstructured.Unstructured{}
obj.SetGroupVersionKind(schema.GroupVersionKind{"example.com", "v1", "MyKind"})
_, err := manager.New(cfg, manager.Options{
	NewCache: cache.BuilderWithOptions(cache.Options {
		ByObject: map[client.Object]cache.ByObject{
			obj: cache.ByObject{}
		},
	})
})

[inteon]

LGTM

[k8s-ci-robot]

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