feat(python): allows to use prj. vars

[devmessias]

resolves #
Resolves dbt-labs/dbt-core#5617, Resolves dbt-labs/dbt-core#10914

Problem

Python models are not friendly when we need to use project variables. This will allow to use project variables without to define that inside the model.yaml

Solution

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development, and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc.) or this PR has already received feedback and approval from Product or DX

[github-actions]

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[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the contributing guide.