[Feature] make `flags:` list strict

[graciegoheen]

Describe the feature

Today, dbt accepts anything and everything in project level flags:. We're just checking for raw yaml https://github.com/dbt-labs/fs/blob/d4190527bdc08f77aa2f2bd30fc7cacff2b0b21f/fs/sa/crates/dbt-schemas/src/schemas/project/dbt_project.rs#L167

If I set a custom flag:

flags:
  grace: is_cool

dbt continues with no warning or error.

This makes it unclear what's "official" dbt-code vs. "my custom thing".

If we wanted to introduce a new dbt flag, we'd risk conflicting with an existing custom flag someone had set in their project.

We should instead make flags: a strict list, and warn or error if you set something that dbt doesn't recognize.

[QMalcolm]

These are all the flags we need to take in account

• https://docs.getdbt.com/reference/global-configs/about-global-configs#common-flag-examples
• https://docs.getdbt.com/reference/global-configs/behavior-changes#dbt-core-behavior-changes
• https://docs.getdbt.com/reference/global-configs/databricks-changes
• https://docs.getdbt.com/reference/global-configs/bigquery-changes
• https://docs.getdbt.com/reference/global-configs/redshift-changes
• https://docs.getdbt.com/reference/global-configs/snowflake-changes

[pugarte7]

Hi! Sounds like an interesting feature to work on. Do I need to get it assigned or can I just work on it and submit the PR? Thanks!