Imporve healing and reporting (#11312)

* Provide information on *actively* healing, buckets healed/queued, objects healed/failed.
* Add concurrent healing of multiple sets (typically on startup).
* Add bucket level resume, so restarts will only heal non-healed buckets.
* Print summary after healing a disk is done.

pkg/madmin/examples/heal-status.go

@@ -21,6 +21,7 @@ package main
 
 import (
 	"context"
+	"encoding/json"
 	"log"
 
 	"github.com/minio/minio/pkg/madmin"
@@ -41,6 +42,7 @@ func main() {
 	if err != nil {
 		log.Fatalln(err)
 	}
+	js, _ := json.MarshalIndent(healStatusResult, "", "  ")
 
-	log.Printf("Heal status result: %+v\n", healStatusResult)
+	log.Printf("Heal status result: %s\n", string(js))
 }