The Metadata module cannot disable writing files

[zonghaishang]

• I have searched the issues of this repository and believe that this is not a duplicate.
• I have checked the FAQ of this repository and believe that this is not a duplicate.

Environment

• Dubbo version: >= 2.7.9
• Operating System version: xxx
• Java version: xxx

Steps to reproduce this issue

1. xxx
2. xxx
3. xxx

Pls. provide [GitHub address] to reproduce this issue.

Expected Result

What do you expected from the above steps？

Actual Result

What actually happens?

Should you decide that file=N/A means disabled?

If there is an exception, please attach the exception trace:

Just put your stack trace here!

[icankeep]

It already supports not writing files when file = N/A