[Feature] Add support for PG16 primary slot on hot standby

[maximvf]

Case: a DBA uses new PG16 feature to configure logical replication from standby per 49.2.2. Replication Slots.

Problem: after the first failover or switchover the only replication slot is lost and subscriptions to standby are to be manually recreated.

Proposed solution: starting with PG16, copy and sync active/running slots from hot standby to other nodes. Destinations could be primary and/or other replicas by list.