[Docs] Adding link at the docs sidebar for PR preview link page (#2895)

This pull request makes a minor update to the documentation sidebar
configuration. The change adds a new guide to the plugin and theme
developer documentation section.

* Added `'main/guides/github-action-pr-preview'` to the sidebar list in
`packages/docs/site/sidebars.js`, making the new GitHub Action PR
Preview guide accessible in the documentation navigation.
* Added Portuguese, Spanish, and French translations.

<img width="1752" height="885" alt="Screenshot 2025-11-13 at 20 32 29"
src="https://github.com/user-attachments/assets/ecff1a6b-1f59-4066-995f-57fe0e34ce51"
/>

Author: fellyph