fix(acme): request certificates for the extra domains too

Instead of just making it _possible_ to perform the name validation...

mail-server/nginx.nix

@@ -48,9 +48,12 @@ in
           };
         };
 
-        security.acme.certs."${cfg.acmeCertificateName}".reloadServices = [
-          "postfix.service"
-          "${dovecotUnitName}.service"
-        ];
+        security.acme.certs."${cfg.acmeCertificateName}" = {
+          extraDomainNames = cfg.certificateDomains;
+          reloadServices = [
+            "postfix.service"
+            "${dovecotUnitName}.service"
+          ];
+        };
       };
 }