fix(transport/http): Add user agent to request headers (#3050)

Fixes #3049

Author: enocom

transport/http/dial.go

@@ -105,6 +105,9 @@ func newClientNewAuth(ctx context.Context, base http.RoundTripper, ds *internal.
 	if ds.RequestReason != "" {
 		headers.Set("X-goog-request-reason", ds.RequestReason)
 	}
+	if ds.UserAgent != "" {
+		headers.Set("User-Agent", ds.UserAgent)
+	}
 	client, err := httptransport.NewClient(&httptransport.Options{
 		DisableTelemetry:      ds.TelemetryDisabled,
 		DisableAuthentication: ds.NoAuth,