Evaluate the Astro 6 Beta

Announcement: https://astro.build/blog/astro-6-beta/

I don't think the breaking changes affect us much, so I'm hoping this will be fairly seamless. I will note that the [Live Collections](https://v6.docs.astro.build/en/guides/content-collections/#live-content-collections) are particularly interesting as we consider moving to Headless CMSs for more of the content.