Add telegraf_output selector for InfluxDB/Postgres dual-write

Introduces global.telegraf_output (INFLUXDB|POSTGRES|BOTH, default BOTH)
so Telegraf can write metrics to Postgres alongside or instead of
InfluxDB. Each minion authenticates with its own so_telegraf_<minion>
role and writes to a matching schema inside a shared so_telegraf
database, keeping blast radius per-credential to that minion's data.

- Per-minion credentials auto-generated and persisted in postgres/auth.sls
- postgres/telegraf_users.sls reconciles roles/schemas on every apply
- Firewall opens 5432 only to minion hostgroups when Postgres output is active
- Reactor on salt/auth + orch/telegraf_postgres_sync.sls provision new
  minions automatically on key accept
- soup post_to_3.1.0 backfills users for existing minions on upgrade
- so-show-stats prints latest CPU/mem/disk/load per minion for sanity checks
- so-telegraf-trim + nightly cron prune rows older than
  postgres.telegraf.retention_days (default 14)

salt/firewall/map.jinja

@@ -55,4 +55,16 @@
 
 {% endif %}
 
+{# Open Postgres (5432) to minion hostgroups when Telegraf is configured to write to Postgres #}
+{% set TG_OUT = (GLOBALS.telegraf_output | default('INFLUXDB')) | upper %}
+{% if TG_OUT in ['POSTGRES', 'BOTH'] %}
+{%   if role.startswith('manager') or role == 'standalone' or role == 'eval' %}
+{%     for r in ['sensor', 'searchnode', 'heavynode', 'receiver', 'fleet', 'idh', 'desktop', 'import'] %}
+{%       if FIREWALL_DEFAULT.firewall.role[role].chain["DOCKER-USER"].hostgroups[r] is defined %}
+{%         do FIREWALL_DEFAULT.firewall.role[role].chain["DOCKER-USER"].hostgroups[r].portgroups.append('postgres') %}
+{%       endif %}
+{%     endfor %}
+{%   endif %}
+{% endif %}
+
 {% set FIREWALL_MERGED = salt['pillar.get']('firewall', FIREWALL_DEFAULT.firewall, merge=True) %}