Explore content layer

[morekid]

Context: #55 (comment)
Experiment: #118

[blaine-arcjet]

Ref https://5-0-0-beta.docs.astro.build/en/guides/content-collections/
and https://docs.astro.build/en/reference/configuration-reference/#creating-a-loader

[blaine-arcjet]

I created a non-working prototype of some changes at https://github.com/arcjet/arcjet-docs/tree/phated/everything-is-broken. My findings were mostly that content layer doesn't work well with things that need to b analyzed statically (such as frontmatter, mdx, etc) since the static analysis happens before rendering.

The branch is useful because it explored some techniques with writing our own remark plugins to augment the static analysis.