[CT-2282] Determine how to favor attributes from dbt_project.yml over those form CLI flags or env vars

[stu-k]

Details

After looking at #6882, the execution team determined that we probably removed the capability of using fields set in dbt_project.yml in our Flags object that we pass around. The way to reintroduce this capability is unclear, so a spike seems appropriate.

Questions

• How did dbt combine fields from both dbt_project.yml and the dbt.flags module before the feature/click-cli branch was merged?
• Is there a way within our current system to respect fields from both dbt_project.yml and those passed in via flags/env vars before initialization of things that require Flags?

[gshank]

The flags module didn't look at dbt_project.yml at all when instantiating flags, just fyi. When those fields were set in the Project they did: target_path: str = flag_or(flags.TARGET_PATH, cfg.target_path, "target"). So the flags version took precedence over the dbt_project.yml setting.

[jtcohen6]

Closing as this is already working (with back compat) in the main branch. All we need in v1.5 is a deprecation warning. We plan to remove this back compat in a future version of dbt-core.