Support GCP universe domain option

[sdanniel]

This is a new feature request for supporting the WithUniverseDomain option in GCP API.

The capability to override the universe domain is needed to support all GCP APIs, including: cloud logging, Pubsub and GCE.

Suggested implementation:

Since the logger.go module already supports few flags (for example) and is imported by multiple other modules, the most straightforward implementation would be to add an additional startup flag to the logger.go and export this flag as a public property.