hosts (latitude-7280): Add disko setup

This prepares for using disko for formatting disks. This switches
from ext4 to btrfs in order to more easily adopt impermanence some
time in the future (see #16).

This disko configuration is at this point not imported anywhere.
I first need to boot using a live medium and then format the disk
using this configuration. Only then I can use this as my disk
configuration file.

Part of #15

hosts/latitude-7280/disko.nix

@@ -0,0 +1,65 @@
+# Disko configuration for formatting the main disk, see https://github.com/nix-community/disko
+# Most of this originates from https://www.youtube.com/watch?v=YPKwkWtK7l0
+# and https://github.com/katexochen/nixos/blob/f931172d272faa2e15a08d757edf9a6072527d02/modules/disko/btrfs-luks.nix
+{device ? throw "Set this to your disk device, e.g. /dev/sda", ...}: let
+  btrfsMountOpts = ["compress=zstd" "noatime"];
+in {
+  disko.devices = {
+    disk.main = {
+      inherit device;
+      type = "disk";
+      content = {
+        type = "gpt";
+        partitions = {
+          esp = {
+            size = "512M";
+            type = "EF00";
+            content = {
+              type = "filesystem";
+              format = "vfat";
+              mountpoint = "/boot";
+              mountOptions = ["default"];
+            };
+          };
+          swap = {
+            size = "8G";
+            content = {
+              type = "swap";
+              resumeDevice = true;
+            };
+          };
+          luks = {
+            size = "100%";
+            content = {
+              type = "luks";
+              name = "crypted";
+              extraOpenArgs = ["--allow-discards"];
+              askPassword = true;
+              content = {
+                type = "btrfs";
+                extraArgs = ["-f"];
+                askPassword = true;
+                content = {
+                  subvolumes = {
+                    "@" = {
+                      mountpoint = "/";
+                      mountOptions = btrfsMountOpts;
+                    };
+                    "@nix" = {
+                      mountpoint = "/nix";
+                      mountOptions = btrfsMountOpts;
+                    };
+                    "@persist" = {
+                      mountpoint = "/persist";
+                      mountOptions = btrfsMountOpts;
+                    };
+                  };
+                };
+              };
+            };
+          };
+        };
+      };
+    };
+  };
+}