fix: Speed up multi-object delete by taking bulk locks (#8974)

Change distributed locking to allow taking bulk locks
across objects, reduces usually 1000 calls to 1.

Also allows for situations where multiple clients sends
delete requests to objects with following names

```
{1,2,3,4,5}
```

```
{5,4,3,2,1}
```

will block and ensure that we do not fail the request
on each other.

cmd/iam.go

@@ -337,14 +337,6 @@ func (sys *IAMSys) Load() error {
 
 // Perform IAM configuration migration.
 func (sys *IAMSys) doIAMConfigMigration(objAPI ObjectLayer) error {
-	// Take IAM configuration migration lock
-	lockPath := iamConfigPrefix + "/migration.lock"
-	objLock := objAPI.NewNSLock(context.Background(), minioMetaBucket, lockPath)
-	if err := objLock.GetLock(globalOperationTimeout); err != nil {
-		return err
-	}
-	defer objLock.Unlock()
-
 	return sys.store.migrateBackendFormat(objAPI)
 }