* add MessagingMode (Edge, Core) in messaging_conf
* move LogosDeliveryMode (Edge, Core, Fleet) to logos_delivery_conf
* applyMode and toWakuNodeConf take MessagingMode
* applyMode can no longer fail; drop its Result
* move MessagingClientConf to api/conf/messaging_conf
* move ReliableChannelManagerConf to new api/conf/channels_conf
* impl modules now import their conf module, not the reverse
* logos_delivery_conf uses channels_conf, not reliable_channel_manager
* cleanup import lists