Reference sources directly in the frontmatter

[benyn]

Description

It'd be great to be able to reference source queries directly in the frontmatter of a Page. This could be part of #2406 , or a separate quick feature since that sounds like a major change.

What problem would this solve?

Referencing sources directly would help avoid repetitive boilerplate queries like:

select * from source_name.source_query_name

This problem is slightly alleviated if you create a .sql file under queries/ and reference it in the frontmatter, but this approach leads to too many middlemen, i.e., those .sql files.

How should it work?

Either being able to refer to source queries like this

---
queries:
  - query_alias: source_1_name/source_query_1_name.sql
  - source_2_name/source_query_2_name.sql
---

or to avoid confusion

---
sources:
  - alias: source_1_name/source_query_1_name.sql
  - source_2_name/source_query_2_name.sql
---