[Dovecot] Add doveadm service

data/conf/dovecot/dovecot.conf

@@ -34,6 +34,12 @@ passdb {
   args = /usr/local/etc/dovecot/sql/dovecot-mysql.conf
   driver = sql
 }
+# Set doveadm_password=your-secret-password in data/conf/dovecot/extra.conf (create if missing)
+service doveadm {
+  inet_listener {
+    port = 12345
+  }
+}
 namespace inbox {
   inbox = yes
   location =