feat: add agenix for secrets management

secrets/secrets.nix

@@ -0,0 +1,20 @@
+# This file is not imported into your NixOS configuration. It is only used for the agenix CLI.
+
+let
+  # get user's ssh public key by command:
+  #     cat ~/.ssh/id_ed25519.pub
+  # if you do not have one, you can generate it by command:
+  #     ssh-keygen -t ed25519
+  ryan = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIJx3Sk20pLL1b2PPKZey2oTyioODrErq83xG78YpFBoj";
+  users = [ ryan ];
+
+  # get system's ssh public key by command:
+  #    cat /etc/ssh/ssh_host_ed25519_key.pub
+  msi-rtx4090 = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAICGeXNCazqiqxn8TmbCRjA+pLWrxwenn+CFhizBMP6en root@msi-rtx4090";
+  systems = [ msi-rtx4090 ];
+in
+{
+  "./encrypt/wg-business.conf.age".publicKeys = users ++ systems;
+  "./encrypt/smb-credentials.age".publicKeys = users ++ systems;
+  # "./encrypt/secret123.age".publicKeys = [ user1 system1 ];
+}