Support self-referencing variables in YAML

[adlersantos]

Description

In order to DRY out values commonly specified in a YAML config (e.g. the dataset name or Airflow data folder), let’s support self-referencing variables in YAML. This is a similar mechanism to Serverless, where you can reference values enclosed in ${} brackets within a YAML configuration

Checklist

• [x] I created this issue in accordance with the Code of Conduct.
• [x] This issue is appropriately labeled.