[Feature] allow incremental_predicates to support self-referential subqueries

[graciegoheen]

Is this your first time submitting a feature request?

• I have read the expectations for open source contributors
• I have searched the existing issues, and I could not find an existing issue for this feature
• I am requesting a straightforward extension of existing dbt functionality, rather than a Big Idea better suited to a discussion

Describe the feature

https://dev.to/superpayments/improve-dbt-incremental-performance-on-snowflake-using-custom-incremental-strategy-3ag3

User wants to limit the incremental logic to only consider the last 24 hours, but incremental_predicates doesn't support self-referential subqueries out-of-the-box, so they inserted their own string substitution logic in the middle by using a custom incremental strategy.

Relevant code

• custom strategy by user
• get_incremental_delete_insert_sql
• snowflake__get_delete_insert_merge_sql
• get_delete_insert_merge_sql