Separate brut frontmatter from custom frontmatter

[robinmetral]

Depending on the project, frontmatter objects can get pretty big and there are essentially two kind of keys:

• things used by brut (template, published_date, permalink, title, buildScript¹, possibly others like is_draft, excerpt, or updated_date in the future, etc.)
• custom frontmatter (e.g. featured_image, subtitle)

It would be nice to isolate one from the other. It makes things clearer and avoids scenarios where brut introduces a new key that clashes with an existing custom one.

Custom frontmatter could be under data for example:

title: My post
published_date: 2024-08-16
data:
  subtitle: Look at what I wrote today
  featured_image: cat.jpg

(Inspired by Cobalt again: cobalt-org/cobalt.rs#257)

Footnotes

1. this might get deprecated soon ↩