Enable garbage collection of custom resources

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.

hack/make-rules/test-integration.sh

@@ -71,7 +71,7 @@ runTests() {
   make -C "${KUBE_ROOT}" test \
       WHAT="${WHAT:-$(kube::test::find_integration_test_dirs | paste -sd' ' -)}" \
       GOFLAGS="${GOFLAGS:-}" \
-      KUBE_TEST_ARGS="${KUBE_TEST_ARGS:-} ${SHORT:--short=true} --vmodule=garbage*collector*=6 --alsologtostderr=true" \
+      KUBE_TEST_ARGS="${KUBE_TEST_ARGS:-} ${SHORT:--short=true} --alsologtostderr=true" \
       KUBE_RACE="" \
       KUBE_TIMEOUT="${KUBE_TIMEOUT}" \
       KUBE_TEST_API_VERSIONS="$1"