Updates about the unworking `CREATE SCHEMA IF NOT EXISTS`

I think this title should be updated because it may concern other editable data such as the password and short links.
For instance "Preserving user-created data".

With a small intro text such as
"To prevent data modified by the users (such as editable layers features or short permalinks) from being lost when redeploying the DB, such data must be saved in dedicated schemas that won't be replaced."