feat: add PuppetDB read-only database user and pooler

PuppetDB requires a separate read-only database user for its read pool.
Without it, it refuses to use the write user for read queries and all
/pdb/query/v4 calls fail with a 500.

- Add puppetdb_read role via CNPG managed.roles with password sourced
  from a new postgres-read-credentials Vault secret
- Grant CONNECT, USAGE, SELECT and default privileges to puppetdb_read
  via postInitApplicationSQL (must also be run manually on existing cluster)
- Add puppet-postgres-pooler-ro Pooler (type: ro) routing to replicas
- Add puppetdb-read-database-conf ConfigMap with read-database.conf
  mounted into /etc/puppetlabs/puppetdb/conf.d/ in the PuppetDB deployment
- Wire OPENVOXDB_READ_POSTGRES_* env vars from the new secret

💘 Generated with Crush

Assisted-by: Claude Sonnet 4.6 via Crush <crush@charm.land>

apps/base/puppet/deployment_puppetdb.yaml

@@ -59,6 +59,16 @@ spec:
                 secretKeyRef:
                   key: username
                   name: postgres-credentials
+            - name: OPENVOXDB_READ_POSTGRES_PASSWORD
+              valueFrom:
+                secretKeyRef:
+                  key: password
+                  name: postgres-read-credentials
+            - name: OPENVOXDB_READ_POSTGRES_USER
+              valueFrom:
+                secretKeyRef:
+                  key: username
+                  name: postgres-read-credentials
           securityContext:
             allowPrivilegeEscalation: false
             capabilities:
@@ -78,6 +88,9 @@ spec:
           volumeMounts:
             - mountPath: /opt/puppetlabs/server/data/puppetdb
               name: puppetdb-storage
+            - mountPath: /etc/puppetlabs/puppetdb/conf.d/read-database.conf
+              name: puppetdb-read-database-conf
+              subPath: read-database.conf
       initContainers:
         - name: create-log-dir
           image: docker.io/busybox:1.37
@@ -154,3 +167,6 @@ spec:
         - name: puppetdb-storage
           persistentVolumeClaim:
             claimName: puppetserver-puppetdb-claim
+        - name: puppetdb-read-database-conf
+          configMap:
+            name: puppetdb-read-database-conf