Automatic merge from submit-queue

[GarbageCollector] Allow per-resource default garbage collection behavior

What's the bug:
When deleting an RC with `deleteOptions.OrphanDependents==nil`, garbage collector is supposed to treat it as `deleteOptions.OrphanDependents==true", and orphan the pods created by it. But the apiserver is not doing that.

What's in the pr:
Allow each resource to specify the default garbage collection behavior in the registry. For example, RC registry's default GC behavior is Orphan, and Pod registry's default GC behavior is CascadingDeletion.