heal: Add MRF metrics to background heal API response (#12398)

This commit gathers MRF metrics from 
all nodes in a cluster and return it to the caller. This will show information about the 
number of objects in the MRF queues 
waiting to be healed.

cmd/server-main.go

@@ -537,6 +537,7 @@ func serverMain(ctx *cli.Context) {
 	// Enable background operations for erasure coding
 	if globalIsErasure {
 		initAutoHeal(GlobalContext, newObject)
+		initHealMRF(GlobalContext, newObject)
 		initBackgroundTransition(GlobalContext, newObject)
 	}