remove strict persistence requirements for List() .metacache objects (#17917)

.metacache objects are transient in nature, and are better left to
use page-cache effectively to avoid using more IOPs on the disks.

this allows for incoming calls to be not taxed heavily due to
multiple large batch listings.

cmd/storage-rest-common.go

@@ -84,4 +84,5 @@ const (
 	storageRESTGlob           = "glob"
 	storageRESTScanMode       = "scan-mode"
 	storageRESTMetrics        = "metrics"
+	storageRESTNoPersistence  = "no-persistence"
 )