heal: Reduce whitespace ticker to 5 seconds (#11234)

30 seconds white spaces is long for some setups which time out when no
read activity in short time, reduce the subnet health white space ticker
to 5 seconds, since it has no cost at all.

cmd/admin-handlers.go

@@ -1412,7 +1412,7 @@ func (a adminAPIHandlers) HealthInfoHandler(w http.ResponseWriter, r *http.Reque
 
 	}()
 
-	ticker := time.NewTicker(30 * time.Second)
+	ticker := time.NewTicker(5 * time.Second)
 	defer ticker.Stop()
 
 	for {