Replace deprecated option.WithCredentialsJSON with secure alternative #2780
Description
We're using the deprecated option.WithCredentialsJSON in connection/check.go for GCP/GCS connection validation.
This is flagged by staticcheck (SA1019) due to security risks with inline JSON credentials.
Fix: Refactor to use option.WithCredentialsFile() with temp files instead.
Temporarily excluded from linting in .golangci.yml - remove once fixed.