feat: add SMTP submission listener and enhance stalwart configuration

- add SMTP submission listener on port 587 with TLS requirement
- configure HAProxy frontend/backend for submission with send-proxy-v2 support
- add dynamic HAProxy node discovery for proxy trusted networks
- use service hostname instead of node FQDN for autoconfig/autodiscover
- remove redundant IMAP/IMAPS/SMTP alt-names from TLS certificates
- update VRRP CNAME configuration to use mail.main.unkin.net

hieradata/country/au/region/syd1/infra/halb/haproxy2.yaml

@@ -13,8 +13,7 @@ profiles::haproxy::dns::vrrp_cnames:
   - dashboard.ceph.unkin.net
   - mail-webadmin.main.unkin.net
   - mail-in.main.unkin.net
-  - imap.main.unkin.net
-  - imaps.main.unkin.net
+  - mail.main.unkin.net
   - autoconfig.main.unkin.net
   - autodiscover.main.unkin.net
 
@@ -365,6 +364,20 @@ profiles::haproxy::backends:
       tcp-check:
         - connect port 25
         - expect string "220 "
+  be_stalwart_submission:
+    description: Backend for Stalwart SMTP Submission
+    collect_exported: false
+    options:
+      mode: tcp
+      balance: roundrobin
+      option:
+        - tcp-check
+        - prefer-last-server
+      stick-table: 'type ip size 200k expire 30m'
+      stick: 'on src'
+      tcp-check:
+        - connect port 587
+        - expect string "220 "
 
 profiles::haproxy::certlist::enabled: true
 profiles::haproxy::certlist::certificates: