Enable airflow stable api for gcp

Description:

Enable stable API for gcp. Minor refactoring & unhardcode integration tests.

# Changes include:
- [x] Refactor (a non-breaking change that improves code maintainability).
- [ ] Bugfix (a non-breaking change that solves an issue).
- [x] New feature (a non-breaking change that adds functionality).
- [ ] Breaking change (a change that is not backward-compatible and/or changes current functionality).
 
# Changes in:
- [x] GCP
- [ ] Azure
- [ ] AWS
- [ ] IBM
 
# Dev Checklist:
- [ ] Added Unit Tests, wherever applicable.
- [ ] Updated the Readme, if applicable.
- [x] Existing Tests pass
- [x] Verified functionality locally
- [x] Self Reviewed my code for formatting and complex business logic.