Expose resource metrics as part of YarnClusterMetrics

Right now, the YarnClusterMetrics just has the total number of node managers returned in it (when queried from a Client -> RM).

It would be useful to also expose NodeManager resource capacities and scheduler max/min resource limits over it to allow clients to pre-determine or pre-compute runtime feasibility without having to request an Application first to get some of this information.

This does not need to be an incompatible change, and we can continue exposing the same values as part of the GetNewApplicationResponse too.