Add `ya.clipboard()` API documentation

[sxyazi]

Add this API to the https://yazi-rs.github.io/docs/plugins/utils page.

See sxyazi/yazi#964 and sxyazi/yazi#980 for details.

[AnirudhG07]

I think this issue can be closed now?

[github-actions]

I'm going to lock this issue because it has been closed for 30 days. ⏳ This helps our maintainers find and focus on the active issues. If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.