Upgrade nit app to support both Testnet and Mainnet

[sync-by-unito]

User story:

As a Numbers user, I want to be able to choose Testnet/Mainnet on nit app so that I can use nit App to test and really register my assets.

┆Issue is synchronized with this Asana task by Unito
┆Created By: Tammy Yang

[sync-by-unito]

➤ Tammy Yang commented:

Let's focus on storage backend migration first