Google Cloud Connection support for non-environmental proxy

### Description

Ability to pass a non-environmental proxy variable to a big query hook connection as it seems to be supported by the underlying package

### Use case/motivation

Setting the proxy at an environmental level can cause unintended conflicts with other packages so it would be beneficial to be able to pass it to the hook

### Related issues

_No response_

### Are you willing to submit a PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)