allow specifying lower disks for Walk() (#17829)

useful when you may want Walk() with
reduced quorum requirements.

cmd/object-api-interface.go

@@ -97,6 +97,8 @@ type ObjectOptions struct {
 
 	WalkFilter      func(info FileInfo) bool // return WalkFilter returns 'true/false'
 	WalkMarker      string                   // set to skip until this object
+	WalkLatestOnly  bool                     // returns only latest versions for all matching objects
+	WalkAskDisks    string                   // dictates how many disks are being listed
 	PrefixEnabledFn func(prefix string) bool // function which returns true if versioning is enabled on prefix
 
 	// IndexCB will return any index created but the compression.