Adding support for Google AuthManager

[rambleraptor]

Rationale for this change

Matches this Java PR

Google's authentication for BigQuery involves using different authentication methods than the current AuthManagers support. This allows users to authenticate against the BigLake REST Catalog (formerly known as the BigQuery REST Catalog)

The GoogleAuthManager introduces authentication methods that are more convenient for GCP users, differing from the generic OAuth2 flow:

• Application Default Credentials (ADC) Support: Provides out-of-the-box, zero-configuration authentication when the Iceberg client runs within GCP environments (e.g., Compute Engine, GKE, Cloud Functions). This is a significant usability improvement over manually setting up OAuth2 parameters.
• Service Account Key File Support: Allows users to authenticate by directly providing a path to a GCP service account JSON key file. This is a common and secure way to authenticate applications with GCP services, and is more specific than the generic token or client secret mechanisms.
• Configurable OAuth Scopes: While the generic OAuth2Manager also supports scopes, GoogleAuthManager defaults to scopes commonly used for GCP services and allows easy customization via the gcp.auth.scopes property.

Are these changes tested?

Unit tests included.

Are there any user-facing changes?

Adds support for Google authentication

[Fokko]

Thanks for adding this @rambleraptor 🙌

I'm not too familiar with the Google Auth system. WDYT @talatuyarer?

[Fokko]

Should we define this as an extra?

[talatuyarer]

I'm not too familiar with the Google Auth system. WDYT @talatuyarer?

Let me try the PR on my local machine @Fokko