* feat: GCP authentication
Add authentication support for:
- authentication with service account key
- authentication with impersonating service account key
- authentication with application default credentials which are read from the environment
A HTTP client with a token set will be returned and used for authentication with all clients. for example
```
gcpClient, err := gcpConfig.GetClient(ctx)
if err != nil {
log.Fatalf("Failed to get client: %v", err)
}
client, err := computeCloud.NewInstancesRESTClient(ctx, option.WithHTTPClient(gcpClient))
if err != nil {
log.Fatalf("Failed to create client: %v", err)
}
```
Elim Tsiagbey
be892acbd9