messaging_service: Add gossip_digest_ack2 implementation
messaging_service: Add gossip_digest_ack2 implementation

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