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

modules/stalwart/manifests/install.pp

@@ -0,0 +1,11 @@
+# @summary Manages Stalwart Mail Server package installation
+#
+# @api private
+class stalwart::install {
+  assert_private()
+
+  # Install stalwart package (user/group created by package preinstall script)
+  package { 'stalwart':
+    ensure => $stalwart::package_ensure,
+  }
+}