Bump PG slots max_replication_slots / max_wal_senders = 25 (#1037)

* Bump PG slots max_replication_slots / max_wal_senders = 25

To support logical replications and keep 9 units installation possible
+ async replication, we should bump slots count.

Author: taurus-forever

src/charm.py

@@ -2344,6 +2344,8 @@ def update_config(
         self._patroni.bulk_update_parameters_controller_by_patroni({
             "max_connections": max_connections,
             "max_prepared_transactions": self.config.memory_max_prepared_transactions,
+            "max_replication_slots": 25,
+            "max_wal_senders": 25,
             "wal_keep_size": self.config.durability_wal_keep_size,
         })