agenix: fix secrets not being opened on boot

Agenix runs before some partitions are mounted,
one option is to mark those partitions are need for boot:

{
  fileSystems."/home".neededForBoot = true;
}

I choose to copy my ssh key to the root user's HOME,
which is not in a separate partition.

system/secrets.nix

@@ -1,6 +1,6 @@
 { pkgs, ... }: {
   age = {
-    identityPaths = [ "/home/lelgenio/.ssh/id_rsa" ];
+    identityPaths = [ "/root/.ssh/id_rsa" ];
     secrets.lelgenio-cachix.file = ../secrets/lelgenio-cachix.age;
     secrets.monolith-gitlab-runner-thoreb-itinerario-registrationConfigFile.file =
       ../secrets/monolith-gitlab-runner-thoreb-itinerario-registrationConfigFile.age;