Merge pull request #1748 from valentinewallace/2022-10-custom-oms

Support custom onion messages

diff --cc lightning/src/ln/peer_handler.rs
Simple merge

diff --cc lightning/src/onion_message/messenger.rs
Simple merge

diff --cc lightning/src/onion_message/packet.rs
Simple merge

diff --cc lightning/src/util/ser.rs
Simple merge