Muli6sModule should also offer index of lowest cell voltage as telemetry value

As available for Muli6S EX, the Muli6s Module should also offer the index of the lowest cell as a telemetry value to be able to log this during a flight. This would allow the user to check if always the same cell is affected and which one it is. Especially interesting when using multiple packs and cascaded Muli6sM.