Add ft service stats db updates

[DilwoarH]

This pull request introduces several database migrations focused on improving notification tracking and reporting. The main changes include creating a new ft_service_stats table for aggregated notification statistics, enforcing data consistency and indexing on the notifications table, and setting up logical replication support.

Database schema and migration improvements:

Creation of notification statistics table:

• Added a new ft_service_stats table to store aggregated counts of notification statuses by service, template, notification type, and status. This includes appropriate foreign keys, a unique constraint on the dimension columns, and several indexes to support efficient queries.
• Updated the current Alembic head to reference the new migration for ft_service_stats.

Notification table indexing and constraints:

• Enforced NOT NULL on the notification_status column in the notifications table.
• Created a unique, concurrently indexed combination of id and notification_status for the notifications table, and set it as the replica identity for logical replication.

Logical replication support:

• Added a migration to create a logical replication slot named notify_dashboard_replication_slot using the wal2json output plugin, with corresponding downgrade logic.