Support GCP Workload Identity in the repository-gcs plugin

Is your feature request related to a problem? Please describe. Storing snapshots with the repository-gcs plugin requires a gcp service account key that's stored as a kubernetes secret. We'd like to avoid this secret as it requires additional overhead like periodically rotating the secret for security. GCP's Workload Identity feature would be a better alternative that avoids the need for a secret.

Describe the solution you'd like Use GCP's workload identity feature for authentication in the repository-gcs plugin.

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered.

Additional context Add any other context or screenshots about the feature request here.