feat: create stalwart module (#418)

- add stalwart module
- add psql database on the shared patroni instance
- add ceph-rgw credentials to eyaml
- ensure psql pass and s3 access key are converted to sensitive

Reviewed-on: #418

site/roles/manifests/infra/mail/backend.pp

@@ -1,9 +1,14 @@
-# a role to deploy a imap/pop3 backend for mail services
+# roles::infra::mail::backend
+#
+# Configures Stalwart IMAP backend servers in a clustered configuration
+# with PostgreSQL for data/fts/memory storage and S3/Ceph-RGW for blob storage.
+# Integrates with postfix hosts for SMTP relay functionality.
+#
 class roles::infra::mail::backend {
   if $facts['firstrun'] {
     include profiles::defaults
     include profiles::firstrun::init
-  }else{
+  } else {
     include profiles::defaults
     include profiles::base
   }