messaging_service: Add gossip_digest_syn implementation
messaging_service: Add gossip_digest_syn implementation

raphaelsc/scylla,scylladb/scylla,avikivity/scylla,duarten/scylla,duarten/scylla,kjniemi/scylla,avikivity/scylla,avikivity/scylla,duarten/scylla,scylladb/scylla,raphaelsc/scylla,scylladb/scylla,scylladb/scylla,raphaelsc/scylla,kjniemi/scylla,kjniemi/scylla