Make the balanced field in /pools/default a public API

For managed deployments like Kubernetes we need to be able to tell if the cluster is currently balanced or if we need to rebalance so that we can make a decision on whether a rebalance needs to be run or not. Currently the easiest way to do this is with the balanced parameter in /pools/default, but my understanding is that this is not a reliable indicator nor is it meant for external use. We would like this to become a public field that we can use or would like a way for us to know whether or not the cluster is balanced.