Adds a new column named `deleted` to the table `activity_center_notifications`.
Related PR in Mobile https://github.com/status-im/status-mobile/pull/15106 for a lot more details of the feature.
Why? Relying on the `dismissed` column for soft deletion is no longer viable because the mobile & desktop clients should display dismissed notifications (sometimes), hence the need for a new column to truly represent soft deletion.
Icaro Motta