Add a way to print resource limits and current consumption

What

It would be useful to have a way to inspect resource manager limits and current consumption in a go-libp2p host. This could help with debugging and monitoring.

How I currently do it

rm := h.Network().ResourceManager()
rm.ViewSystem(
	func(rs network.ResourceScope) error {
		fmt.Printf("stats: %+v\n", rs.Stat())
		if r, ok := rs.(interface{ Limit() rcmgr.Limit }); ok {
			fmt.Printf("limits: %+v\n", r.Limit())
		}
		return nil
	},
)

Start with the Go resource-manager access point shown in the issue: h.Network().ResourceManager().Read the ViewSystem callback and the ResourceScope Stat and Limit interfaces to understand the existing inspection data. Done means a host can expose resource-manager limits and current consumption through a documented, usable mechanism; the payload names no tests or files to run.