feat(systems): enable email notifications on failure

- Added `emailOnFailure.enable` option to metacfg with a default of `false`.
- Enabled email notifications on failure for SGX and MX systems.
- Enhanced `systemd-email-notify` module to support the new configuration.

modules/nixos/services/systemd-email-notify/default.nix

@@ -4,10 +4,11 @@
   pkgs,
   ...
 }:
-
 with lib;
-
+with lib.metacfg;
 let
+  cfg = config.metacfg.emailOnFailure;
+
   checkConditions = pkgs.writeScript "checkConditions" ''
     #!/bin/sh
     STATUS=$(systemctl status --full "$1")
@@ -34,6 +35,10 @@ let
 in
 {
   options = {
+    metacfg.emailOnFailure = with types; {
+      enable = mkBoolOpt false "Whether or not to send mails on failure.";
+    };
+
     systemd.email-notify.mailTo = mkOption {
       type = types.str;
       default = "admin";
@@ -55,7 +60,7 @@ in
     };
   };
 
-  config = {
+  config = mkIf cfg.enable {
     systemd.services."email@" = {
       description = "Sends a status mail via sendmail on service failures.";
       onFailure = mkForce [ ];

systems/x86_64-linux/mx/default.nix

@@ -19,6 +19,7 @@
   ];
 
   metacfg = {
+    emailOnFailure.enable = true;
     base.enable = true;
     nix.enable = true;
     podman.enable = true;

systems/x86_64-linux/sgx/default.nix

@@ -21,6 +21,7 @@
   ];
 
   metacfg = {
+    emailOnFailure.enable = true;
     base.enable = true;
     gui.enable = true;
     nix-ld.enable = true;