[Feature] Support Optional Override of dataproc cluster for python models

[matt-winkler]

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-bigquery functionality, rather than a Big Idea better suited to a discussion

Describe the feature

Currently, dbt-bigquery does not support overriding the execution_project for python models. Adding this will enable users to better balance their compute allocations at scale.

Describe alternatives you've considered

Changing environment variables mid-job?

Who will this benefit?

dbt-bigquery users who leverage python models

Are you interested in contributing this feature?

Yes

Anything else?

yee haw