Use actual encryption passwords

dk/single_uefi_btrfs.nix

@@ -1,4 +1,4 @@
-{ id, name, ... }:
+{ id, name, passwordFile ? "/should_not_be_needed_in_this_context", ... }:
 {
   disko.devices = {
     disk = {
@@ -26,7 +26,7 @@
               content = {
                 type = "luks";
                 name = "${name}";
-                passwordFile = "/tmp/secret.key"; # FIXME Generate this somehow
+                passwordFile = passwordFile;
                 settings = {
                   # Not having SSDs die fast is more important than crypto
                   # nerds that could potentially discover which filesystem I