Telemetry doesn't work with non-ADC

[enocom]

If I launch the Proxy with an OAuth2 token or a credentials file while using Telemetry, the Proxy fails to start.

The reason for this is stackdriver does requires that we set non-ADC in the stackdriver.Options struct:

alloydb-auth-proxy/cmd/root.go

Lines 980 to 983 in 5d496b4

	sd, err := stackdriver.NewExporter(stackdriver.Options{
	ProjectID: cmd.conf.TelemetryProject,
	MetricPrefix: cmd.conf.TelemetryPrefix,
	})

In addition, the Proxy should love the error as we've disabled error reporting after parsing the config.