[otel-collector] Document how to export internal collector logs

Extend the [OpenTelemetry internal telemetry Assets](https://github.com/elastic/integrations/tree/main/packages/otel_collector_internal_telemetry/docs) documentation with a sample configuration on how to export the internal logs of collector using `service::telemetry::logs`. This is important to ensure logs are stored in internal telemetry data streams instead of the being collected with the filelog receiver and stored into the generic logs data stream: https://github.com/elastic/elastic-agent/blob/main/deploy/helm/edot-collector/kube-stack/values.yaml#L331