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 send-proxy-v2 support to all listeners
- 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/roles/infra/mail/backend.yaml

@@ -8,9 +8,6 @@ hiera_include:
 profiles::pki::vault::alt_names:
   - mail.main.unkin.net
   - mail-webadmin.main.unkin.net
-  - imap.main.unkin.net
-  - imaps.main.unkin.net
-  - smtp.main.unkin.net
   - main-in.main.unkin.net
   - autoconfig.main.unkin.net
   - autodiscovery.main.unkin.net
@@ -41,6 +38,7 @@ stalwart::s3_region: "%{facts.region}"
 stalwart::domains:
   - 'mail.unkin.net'
 stalwart::postfix_relay_host: 'out-mta.main.unkin.net'
+stalwart::service_hostname: 'mail.main.unkin.net'
 stalwart::manage_dns_records: false
 
 ## With load balancer: