feat: bring new HDD related performance enhancements (#18239)

Optionally allows customers to enable 

- Enable an external cache to catch GET/HEAD responses 
- Enable skipping disks that are slow to respond in GET/HEAD 
  when we have already achieved a quorum

cmd/server-main.go

@@ -840,7 +840,9 @@ func serverMain(ctx *cli.Context) {
 
 		// Initialize data scanner.
 		bootstrapTrace("initDataScanner", func() {
-			initDataScanner(GlobalContext, newObject)
+			if v := env.Get("_MINIO_SCANNER", config.EnableOn); v == config.EnableOn {
+				initDataScanner(GlobalContext, newObject)
+			}
 		})
 
 		// Initialize background replication