encodeGroupAssignment = ({ memberId, memberAssignment }) => {
  return new Encoder().writeString(memberId).writeBytes(memberAssignment)
}
SyncGroup Request (Version: 0) => group_id generation_id member_id [group_assignment]
  group_id => STRING
  generation_id => INT32
  member_id => STRING
  group_assignment => member_id member_assignment
    member_id => STRING
    member_assignment => BYTES