Add a resource fit predicate.

Not linked into any scheduler yet.
See my other comment about self-describing.  Omnibus structures that are used in different contexts make it very hard to reason about things.  I'd much rather start with something like

    type NodeResources struct {
        Capacity ResourceList
        Peak ResourceList
    }

    type PodResourceRequest {
        Request ResourceList
        Limit ResourceList
    }

    type PodResourceReport {
        PodResourceRequest
        Peak ResourceList
    }