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/vaultstaticsecret.yaml

@@ -35,6 +35,23 @@ spec:
 ---
 apiVersion: secrets.hashicorp.com/v1beta1
 kind: VaultStaticSecret
+metadata:
+  name: postgres-read-credentials
+  namespace: puppet
+spec:
+  destination:
+    create: true
+    name: postgres-read-credentials
+    overwrite: true
+  hmacSecretData: true
+  mount: kv
+  path: kubernetes/namespace/puppet/default/postgres-read-credentials
+  refreshAfter: 5m
+  type: kv-v2
+  vaultAuthRef: default
+---
+apiVersion: secrets.hashicorp.com/v1beta1
+kind: VaultStaticSecret
 metadata:
   name: eyaml-keys
   namespace: puppet