Remove JSONB columns in state changes table and replace with typed columns

[aditya1702]

JSONB column is supposed to be helpful when we do not know the key-value pairs beforehand and provides flexibility. However for a lot of our columns, we should directly store the values and return a JSON representation during query time. For e.g. trustline limits, thresholds, flags etc... This saves unnecessary JSONB storage overhead and makes the data model more efficient and easy to deal with.