Configure pam-gnupg

Automatically unlock my GPG key on login to make it easier to work with
pass, neomutt, etc.

See https://github.com/cruegge/pam-gnupg.

modules/mixins/gnupg.nix

@@ -1,11 +1,25 @@
 { pkgs, ... }:
 
 {
+  security.pam.services.login.gnupg.enable = true;
+
   programs = {
     gnupg.agent = {
       enable = true;
       enableSSHSupport = true;
+
       pinentryPackage = pkgs.pinentry-qt;
     };
   };
+
+  home-manager.users.opdavies = {
+    home.file = {
+      ".gnupg/gpg-agent.conf".text = ''
+        allow-preset-passphrase
+        default-cache-ttl 600
+        max-cache-ttl 7200
+        enable-ssh-support
+      '';
+    };
+  };
 }