Split postgres auth from per-minion telegraf creds

The old flow had two writers for each per-minion Telegraf password
(so-minion wrote the minion pillar; postgres.auth regenerated any
missing aggregate entries). They drifted on first-boot and there was
no trigger to create DB roles when a new minion joined.

Split responsibilities:

- pillar/postgres/auth.sls (manager-scoped) keeps only the so_postgres
  admin cred.
- pillar/telegraf/creds.sls (grid-wide) holds a {minion_id: {user,
  pass}} map, shadowed per-install by the local-pillar copy.
- salt/manager/tools/sbin/so-telegraf-cred is the single writer:
  flock, atomic YAML write, PyYAML safe_dump so passwords never
  round-trip through so-yaml.py's type coercion. Idempotent add, quiet
  remove.
- so-minion's add/remove hooks now shell out to so-telegraf-cred
  instead of editing pillar files directly.
- postgres.telegraf_users iterates the new pillar key and CREATE/ALTERs
  roles from it; telegraf.conf reads its own entry via grains.id.
- orch.deploy_newnode runs postgres.telegraf_users on the manager and
  refreshes the new minion's pillar before the new node highstates,
  so the DB role is in place the first time telegraf tries to connect.
- soup's post_to_3.1.0 backfills the creds pillar from accepted salt
  keys (idempotent) and runs postgres.telegraf_users once to reconcile
  the DB.

salt/postgres/auth.sls

@@ -13,24 +13,8 @@
   {% set CHARS = DIGITS~LOWERCASE~UPPERCASE~SYMBOLS %}
   {% set so_postgres_user_pass = salt['pillar.get']('postgres:auth:users:so_postgres_user:pass', salt['random.get_str'](72, chars=CHARS)) %}
 
-  {# Per-minion Telegraf Postgres credentials. Merge currently-up minions with any #}
-  {# previously-known entries in pillar so existing passwords persist across runs. #}
-  {% set existing = salt['pillar.get']('postgres:auth:users', {}) %}
-  {% set up_minions = salt['saltutil.runner']('manage.up') or [] %}
-  {% set telegraf_users = {} %}
-  {% for key, entry in existing.items() %}
-    {%- if key.startswith('telegraf_') and entry.get('user') and entry.get('pass') %}
-      {%- do telegraf_users.update({key: entry}) %}
-    {%- endif %}
-  {% endfor %}
-  {% for mid in up_minions %}
-    {%- set safe = mid | replace('.','_') | replace('-','_') | lower %}
-    {%- set key = 'telegraf_' ~ safe %}
-    {%- if key not in telegraf_users %}
-      {%- do telegraf_users.update({key: {'user': 'so_telegraf_' ~ safe, 'pass': salt['random.get_str'](72, chars=CHARS)}}) %}
-    {%- endif %}
-  {% endfor %}
-
+# Admin cred only. Per-minion Telegraf creds live in telegraf/creds.sls,
+# managed by /usr/sbin/so-telegraf-cred (called from so-minion).
 postgres_auth_pillar:
   file.managed:
     - name: /opt/so/saltstack/local/pillar/postgres/auth.sls
@@ -43,11 +27,6 @@ postgres_auth_pillar:
               so_postgres_user:
                 user: so_postgres
                 pass: "{{ so_postgres_user_pass }}"
-              {% for key, entry in telegraf_users.items() %}
-              {{ key }}:
-                user: {{ entry.user }}
-                pass: "{{ entry.pass }}"
-              {% endfor %}
     - show_changes: False
 {% else %}
 

salt/postgres/telegraf_users.sls

@@ -10,7 +10,7 @@
 
 {# postgres_wait_ready below requires `docker_container: so-postgres`, which is
    declared in postgres.enabled. Include it here so state.apply postgres.telegraf_users
-   on its own (from the reactor orch or from soup) still has that ID in scope. Salt
+   on its own (e.g. from orch.deploy_newnode) still has that ID in scope. Salt
    de-duplicates the circular include. #}
 include:
   - postgres.enabled
@@ -96,9 +96,9 @@ postgres_telegraf_group_role:
     - require:
       - cmd: postgres_create_telegraf_db
 
-{%   set users = salt['pillar.get']('postgres:auth:users', {}) %}
-{%   for key, entry in users.items() %}
-{%     if key.startswith('telegraf_') and entry.get('user') and entry.get('pass') %}
+{%   set creds = salt['pillar.get']('telegraf:postgres_creds', {}) %}
+{%   for mid, entry in creds.items() %}
+{%     if entry.get('user') and entry.get('pass') %}
 {%       set u = entry.user %}
 {%       set p = entry.pass | replace("'", "''") %}