Have masters update DataNode details based on state heartbeats from volume servers. (#8017)

weed/topology/data_node.go

@@ -23,6 +23,8 @@ type DataNode struct {
 	LastSeen      int64 // unix time in seconds
 	Counter       int   // in race condition, the previous dataNode was not dead
 	IsTerminating bool
+
+	MaintenanceMode bool
 }
 
 func NewDataNode(id string) *DataNode {