Fix namespaced bug of node resource, node resource should be a
non-namespaced resource as the resource namespace.
By doing this fix, node resouce can be accessed as expected, as the issue explains.
Closes issue:[#178](https://github.com/DirectXMan12/k8s-prometheus-adapter/issues/178)
This commit introduces advanced configuration. The rate-interval and
label-prefix flags are removed, and replaced by a configuration file
that allows you to specify series queries and the rules for transforming
those into metrics queries and API resources.
