add option for O_SYNC writes for standalone FS backend (#9581)

pkg/ioutil/append-file_windows.go

@@ -24,7 +24,7 @@ import (
 )
 
 // AppendFile - appends the file "src" to the file "dst"
-func AppendFile(dst string, src string) error {
+func AppendFile(dst string, src string, osync bool) error {
 	appendFile, err := lock.Open(dst, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0644)
 	if err != nil {
 		return err