dbt - generate _sources.yml from recipe.yml

[fvankrieken]

Was going to create an issue, but remembered "discussions" exist, and this seemed like a better spot for it!

Basically, while updating sources.yml for gft, I thought that it felt a bit too redundant with the recipe file - we already list all sources there. So why not only have one source of truth for imported data sources?

We'd need to brainstorm a little bit about what we'd want this to look like, but in some ways it'd be nice to just include source validation in a recipe, rather than having to define each source dataset a second time in _sources.yml. Curious to know others thoughts, both on the merits of the idea and potential specifics around implementation (for constraints, do we just use dbt syntax? Do we have "constraint defaults" in recipe, that get applied to all sources? Do we check in _sources.yml, or is it just created ephemerally for builds? etc)

[fvankrieken]

Also, made a dbt issue label - seems like it'll in general be a big enough bucket that it's useful