Add custom impermanence module

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

hosts/common/system/configs/sops/default.nix

@@ -3,7 +3,7 @@
   imports = [ inputs.sops-nix.nixosModules.sops ];
 
   environment = {
-    persistence."/persist".files = [ "/etc/ssh/ssh_host_ed25519_key" ];
+    persistence."/persist"."/etc/ssh/ssh_host_ed25519_key" = { };
     systemPackages = with pkgs; [ sops ];
   };