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/configmap_puppetdb-config.yaml

@@ -17,4 +17,7 @@ data:
   OPENVOXDB_POSTGRES_HOSTNAME: "puppet-postgres-pooler"
   OPENVOXDB_POSTGRES_DATABASE: "puppetdb"
   OPENVOXDB_POSTGRES_PORT: "5432"
+  OPENVOXDB_READ_POSTGRES_HOSTNAME: "puppet-postgres-pooler-ro"
+  OPENVOXDB_READ_POSTGRES_DATABASE: "puppetdb"
+  OPENVOXDB_READ_POSTGRES_PORT: "5432"
   PUPPETDB_JAVA_ARGS: ""