Add scheduler in distance oracle executable

The suggested method to run distance oracle is currently using a cron, which was fine when the delay between executions was more than one hour, but for a delay around minute, it would be better to have Rust schedule itself the execution, as suggested by @tuxmain in https://forum.duniter.org/t/besoin-de-plus-de-forgeron-avec-oracle-de-distance/12669/6.