Prepend Models::ReleaseHighlight for translated `what's new` text in jh

What does this MR do and why?

In this issue(in Jihulab), we need to translate the content in What's New in Jihulab, so we need to change the position of the content fetched in ReleaseHighlight.
We need to prepend_mod this Model::ReleaseHighlight.

And I added a method to override the content directory:whats_new_path.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

/cc @daveliu @zhaoqi01

Edited by LXY

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