Allow optional VK in CR metrics

Allow optional VK in CR metrics, while only requiring the group to be
fixed. This would allow users to define custom metrics for:
* a specific API version: version is fixed, kind varies.
* all the API versions of a resource: version varies, kind is fixed.
* all the APIs part of an API group: version varies, kind varies.

Signed-off-by: Pranshu Srivastava <rexagod@gmail.com>

pkg/customresourcestate/config.go

@@ -161,6 +161,11 @@ type ConfigDecoder interface {
 	Decode(v interface{}) (err error)
 }
 
+// generateResources generates the set of possible resources from the varying V and, or K of the original config.
+func generateResources(r []Resource) []Resource {
+	return nil
+}
+
 // FromConfig decodes a configuration source into a slice of customresource.RegistryFactory that are ready to use.
 func FromConfig(decoder ConfigDecoder) ([]customresource.RegistryFactory, error) {
 	var crconfig Metrics