add missing available space from metrics (#10065)

cmd/erasure.go

@@ -146,6 +146,7 @@ func getDisksInfo(disks []StorageAPI, endpoints []string) (disksInfo []madmin.Di
 				DrivePath:      info.MountPath,
 				TotalSpace:     info.Total,
 				UsedSpace:      info.Used,
+				AvailableSpace: info.Free,
 				UUID:           info.ID,
 				State:          diskErrToDriveState(err),
 			}