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/server-rlimit.go

@@ -24,7 +24,6 @@ import (
 
 func setMaxResources() (err error) {
 	// Set the Go runtime max threads threshold to 90% of kernel setting.
-	// Do not return when an error when encountered since it is not a crucial task.
 	sysMaxThreads, mErr := sys.GetMaxThreads()
 	if mErr == nil {
 		minioMaxThreads := (sysMaxThreads * 90) / 100