Devise a way to add a substorage when new module are deployed

[dynaxis]

Currently just adding an empty substorage for ongoing use is considered a state change, resulting in a new root hash. It means that there must conceptually be a transaction to add a new empty substorage. When we upgrade applications, there might be cases where a new module with its own state is introduced. And this behavior introduces some hassles.

I'm not sure if this problem is solved if we can add an empty substorage without a transaction and the state changes only upon a change to the substorage. But it might be so.

We need to inspect this problem at least when we design the on-chain governance and upgrade scheme.