Add data usage collect with its new admin API (#8553)

Admin data usage info API returns the following

(Only FS & XL, for now)

- Number of buckets
- Number of objects
- The total size of objects
- Objects histogram
- Bucket sizes

cmd/server-main.go

@@ -437,6 +437,7 @@ func serverMain(ctx *cli.Context) {
 		globalObjLayerMutex.Unlock()
 	}
 
+	initDataUsageStats()
 	initDailyLifecycle()
 
 	if globalIsXL {