Autoptimize < 3.1.15 - Contributor+ Stored XSS via 'ao_post_preload' Meta Value

Description

The plugin is vulnerable to Stored Cross-Site Scripting via the 'ao_post_preload' meta value due to insufficient input sanitization in the `ao_metabox_save()` function and missing output escaping when the value is rendered into a `<link>` tag in `autoptimizeImages.php`. This makes it possible for authenticated attackers, with Contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page, granted the "Image optimization" or "Lazy-load images" setting is enabled in the plugin configuration.