Enable hot_standby_feedback on the authentik postgres cluster (#473)

Authentik serves multi-second API reads from the CNPG hot standbys. Those reads outlive `max_standby_streaming_delay`, so recovery cancels them with `canceling statement due to conflict with recovery`, which authentik surfaces as HTTP 500 — enough to break a terraform apply mid-run.

- set `hot_standby_feedback` on so replicas report their oldest xmin to the primary and long reads stop being cancelled
- SIGHUP reload only, no restart or switchover
- retained-dead-tuple cost is negligible on a ~155MB database

Reviewed-on: #473
Co-authored-by: unkin-agent <unkin-agent@unkin.net>
Co-committed-by: unkin-agent <unkin-agent@unkin.net>

apps/base/authentik/cnpg_cluster.yaml

@@ -66,6 +66,10 @@ spec:
       dynamic_shared_memory_type: posix
       effective_cache_size: 256MB
       full_page_writes: "on"
+      # Replicas report their oldest xmin to the primary, so multi-second reads on
+      # a hot standby stop exhausting max_standby_streaming_delay and being
+      # cancelled. Retained-dead-tuple cost is negligible on a ~155MB database.
+      hot_standby_feedback: "on"
       log_destination: csvlog
       log_directory: /controller/log
       log_filename: postgres