Provision SMTP credentials and sender address from mailu

Replace hardcoded SMTP defaults with mailu provisioner — host, port,
user, password, and NOTIFY_FROM all come from the provisioned mailbox.

module.yml

@@ -21,6 +21,16 @@ requires:
       AMQP_USER: user
       AMQP_PASSWORD: password
       AMQP_VHOST: vhost
+  - provider: mailu
+    type: mailbox
+    name: amqp-forwarder
+    node: novox
+    env_map:
+      SMTP_USER: email
+      SMTP_PASSWORD: password
+      SMTP_HOST: smtp_host
+      SMTP_PORT: smtp_port
+      NOTIFY_FROM: email
 
 env:
   AMQP_HOST:
@@ -35,15 +45,12 @@ env:
   AMQP_QUEUE:
     default: "email-forwarder"
   SMTP_HOST:
-    default: "host.docker.internal"
   SMTP_PORT:
-    default: "587"
   SMTP_USER:
   SMTP_PASSWORD:
   NOTIFY_TO:
     default: "jochen.schoubben@mediahuis.be"
   NOTIFY_FROM:
-    default: "jschoubben@novox.be"
 
 package:
   - docker-compose.yml