Implement bulk delete (#7607)

Bulk delete at storage level in Multiple Delete Objects API

In order to accelerate bulk delete in Multiple Delete objects API,
a new bulk delete is introduced in storage layer, which will accept
a list of objects to delete rather than only one. Consequently,
a new API is also need to be added to Object API.

cmd/storage-rest-common.go

@@ -35,6 +35,7 @@ const (
 	storageRESTMethodReadFileStream = "readfilestream"
 	storageRESTMethodListDir        = "listdir"
 	storageRESTMethodDeleteFile     = "deletefile"
+	storageRESTMethodDeleteFileBulk = "deletefilebulk"
 	storageRESTMethodRenameFile     = "renamefile"
 	storageRESTMethodGetInstanceID  = "getinstanceid"
 )