Automatic merge from submit-queue
add generic shared informer backed by existing informer
Adds the ability to get an informer and lister that returns `[]runtime.Object` methods with the "normal" filtering capabilities based on a `GroupResource`. Right now, it only works on known types (and re-uses those caches for efficiency by having a different skin on the `Index`). It should be extended in the future.
@derekwaynecarr I think this gives you the types you were looking for to avoid the ugly array copies.
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