[DWH] get GCP creds from GOOGLE_APPLICATION_CREDENTIALS_FILE env var for DWH client

[commoddity]

🌿 Summary

Update the DWH client to read GCP credentials from the GOOGLE_APPLICATION_CREDENTIALS_FILE environment variable instead of using default application credentials.

🌱 Primary Changes:

• Modified NewDriver function to accept credentials file path parameter
• Added GOOGLE_APPLICATION_CREDENTIALS_FILE environment variable configuration
• Updated main.go to pass the credentials file to the DWH driver constructor

🍃 Secondary changes:

• Added validation to ensure GOOGLE_APPLICATION_CREDENTIALS_FILE is set
• Updated function documentation to explain the credentials fallback behavior
• Enhanced error handling for missing credentials configuration

🛠️ Type of change

Select one or more from the following:

• New feature, functionality or library
• Bug fix
• Code health or cleanup
• Documentation
• Other (specify)

🤯 Sanity Checklist

• I have updated the GitHub Issue 'assignees', 'reviewers', 'labels', 'project', 'iteration' and 'milestone'
• For docs, I have run 'make docusaurus_start'
• For code, I have run 'make test_all'
• For configurations, I have update the documentation
• I added TODOs where applicable