Remove unused physical replication slot from pgBackRest Patroni setup

[ghorbani-ali]

Description

Summary

This PR removes the following permanent physical replication slot from the Patroni configuration example in the pgBackRest setup guide:

slots:
  percona_cluster_1:
    type: physical

Why this change is helpful

The guide currently defines a permanent physical replication slot, but it does not configure a standby or another client to consume it.

If the slot remains inactive, PostgreSQL may continue retaining WAL for it. Over time, this can lead to unexpected growth of the pg_wal directory and, in some cases, increased disk usage.

After setting up pgBackRest for the cluster by following the documentation, this configuration block caused excessive WAL retention. The resulting disk usage eventually filled the available storage and led to a serious outage.

What changed

• Removed the unused percona_cluster_1 physical replication slot from the Patroni configuration example.
• Left use_slots: true unchanged, so Patroni can continue managing replication slots for cluster members.
• Updated the example to better match the guidance shared in the related Percona forum discussions.

References

• Physical replication slot created through Patroni configuration has retained WAL
• Patroni: WAL files are not deleted after pg_restore