Missing fields

When comparing to the [available front matter fields](https://mystmd.org/guide/frontmatter#available-frontmatter-fields) in MyST, there are a few that are currently not being read by *pubmatter*. The list is probably not exhaustive, but these are the ones I've currently run into that are needed:

- `github`
- `parts`
	- `funding`
	- `data_availability`