Implements three metrics for nfd-gc:
- nfd_gc_build_info: version information of nfd-gc.
- nfd_gc_objects_deleted_total: total number of NodeFeature and
NodeResourceTopology objects deleted by nfd-gc.
- nfd_gc_object_delete_failures_total: number of errors encountered when
deleting NodeFeature and NodeResourceTopology objects.
Rename the old "topology-gc" to just "gc". Simplify the setup a bit by
including the RBAC rules in the "gc" base.
Note: we don't enable nfd-gc in the default overlay, yet, as the
NodeFeature API isn't enabled (gc is not needed).
