Add self-healing feature (#7604)

- Background Heal routine receives heal requests from a channel, either to
heal format, buckets or objects
- Daily sweeper lists all objects in all buckets, these objects
don't necessarly have read quorum so they can be removed if
these objects are unhealable
- Heal daily ops receives objects from the daily sweeper
and send them to the heal routine.

cmd/globals.go

@@ -261,6 +261,11 @@ var (
 	// GlobalGatewaySSE sse options
 	GlobalGatewaySSE gatewaySSE
 
+	// The always present healing routine ready to heal objects
+	globalBackgroundHealing *healRoutine
+	globalAllHealState      *allHealState
+	globalSweepHealState    *allHealState
+
 	// Add new variable global values here.
 )