feat: Add Astro content loader to integration guides

[LekoArts]

Hello!

I've recently published https://github.com/LekoArts/astro-loaders/tree/main/packages/plausible which is a loader for Astro's content layer: https://docs.astro.build/en/guides/content-collections/

You can think of the content layer as a database that gets filled up during build by requests that people make inside their pages. This Plausible content loader allows people to query the Stats API v2 during build and then use the data inside a SSG page, so no API calls in the browser.

The whole query interface is type-safe as I converted the information in the docs to a Typescript schema.