The spring onions and bay leaves honestly seem like a waste. Usually you discard the soaking water, and that's going to take most of the already-subtle flavor with it.
So if you want to add flavor, whether with spring onions and bay leaves, spices, or anything else, add it during cooking. The cooking time is plenty long to get all the flavor into the water/broth and beans, and you won't be pouring any of it down the drain.
Baking soda is added during soaking mainly to help soften the beans faster. People will also say it helps reduce gas-causing sugars, and perhaps other reasons, but it's hard to find evidence for them.
Relatedly, many people add salt during soaking to help soften and avoid bursting.