Plugin Directory improvements: add "Live Preview" button

The WordPress.org Plugin Directory is currently testing a new optional "Live Preview" button, powered by WP Playground. That button will appear when you've committed a `blueprint.json` file in `assets/blueprints` in the plugin's SVN.
-- [Plugin Directory: Preview button revisited](https://make.wordpress.org/meta/2023/11/22/plugin-directory-preview-button-revisited/)

That blueprint file offers a few options that could be interesting to automatically set up our plugins for a demo:

- Pre-install plugins
- Pre-install themes
- Set options
- [And more, as explained in the documentation](https://wordpress.github.io/wordpress-playground/blueprints-api/steps)

Let's consider the steps needed for us to prepare the Jetpack plugin for a demo.

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