Before deleting an object based on absent owners, GC verifies absence of those owners with a live lookup.
The coordinates used to perform that live lookup are the ones specified in the ownerReference of the child.
In order to performantly delete multiple children from the same parent (e.g. 1000 pods from a replicaset),
a 404 response to a lookup is cached in absentOwnerCache.
Previously, the cache was a simple uid set. However, since children can disagree on the coordinates
that should be used to look up a given uid, the cache should record the exact coordinates verified absent.
This is a [apiVersion, kind, namespace, name, uid] tuple.
Enhance the garbage collector to periodically refresh the resources it
monitors (via discovery) to enable custom resource definition GC.
This implementation caches Unstructured structs for any kinds not
covered by a shared informer. The existing meta-only codec only supports
compiled types; an improved codec which supports arbitrary types could
be introduced to optimize caching to store only metadata for all
non-informer types.
