Modify the DatabaseHolder::openDb method to check if the new database's name matches any prefix in MigratingTenantAccessBlockerByPrefix (by calling MigratingTenantAccessBlockerByPrefix::get with the database's name), and if so, set the new Database's shared_ptr<MigratingTenantAccessBlocker> decoration to the returned shared_ptr<MigratingTenantAccessBlocker>.

Note that there is no durable concept of a database. A database is created by being "opened", and durable state for it is only created when a collection in it is created.