DATA-1996: adjust the dbt config parser so that view/ephemeral staging layer doesnt need a task

[claudiazi]

Adjust the dbt config parser so that:

• If the node is a DBT source, an Athena table task is generated.
• If the node is an ephemeral model, a dummy task is generated, and tasks for its dependent nodes are recursively generated.
• If the node is a staging model (preparation model) and not materialized as a table, a table task is generated along with tasks for its dependent nodes.
• For other nodes, a table task is generated. If the node is materialized as a table, an additional S3 task is also generated.

Tested in airflow-staging
example:

[swarmia]

✅  Linked to Bug DATA-1996 · Improve the dbt-preparation dag

[kiranvasudev]

lgtm