add '.healing.bin' for tracking currently healing disk (#10573)

add a hint on the disk to allow for tracking fresh disk
being healed, to allow for restartable heals, and also
use this as a way to track and remove disks.

There are more pending changes where we should move
all the disk formatting logic to backend drives, this
PR doesn't deal with this refactor instead makes it
easier to track healing in the future.

cmd/admin-handlers.go

@@ -295,6 +295,20 @@ func (a adminAPIHandlers) StorageInfoHandler(w http.ResponseWriter, r *http.Requ
 	// ignores any errors here.
 	storageInfo, _ := objectAPI.StorageInfo(ctx, false)
 
+	// Collect any disk healing.
+	healing, _ := getAggregatedBackgroundHealState(ctx)
+	healDisks := make(map[string]struct{}, len(healing.HealDisks))
+	for _, disk := range healing.HealDisks {
+		healDisks[disk] = struct{}{}
+	}
+
+	// find all disks which belong to each respective endpoints
+	for i, disk := range storageInfo.Disks {
+		if _, ok := healDisks[disk.Endpoint]; ok {
+			storageInfo.Disks[i].Healing = true
+		}
+	}
+
 	// Marshal API response
 	jsonBytes, err := json.Marshal(storageInfo)
 	if err != nil {