hosts: add iso

This makes it possible to build a custom NixOS installer iso with the
tools I want. Ideally I get to a point where I can use the iso like a
live cd with Hyprland and/or dwm installed with everything already
configured.

Build the iso with the following command:

```
nix build .#nixosConfigurations.iso.config.system.build.isoImage
```

Then, use qemu to test the iso:

```
qemu-system-x86_64 -enable-kvm -m 256 -cdrom ./result/iso/nixos-*
```

flake.nix

@@ -84,6 +84,12 @@
           specialArgs.nix-config = self;
           modules = listFilesRecursive ./hosts/phone;
         };
+
+        iso = nixosSystem {
+          system = "x86_64-linux";
+          specialArgs.nix-config = self;
+          modules = listFilesRecursive ./hosts/iso;
+        };
       };
 
       formatter = forAllSystems (pkgs: pkgs.nixfmt-rfc-style);

hosts/iso/configuration.nix

@@ -0,0 +1,13 @@
+{ pkgs, modulesPath, ... }:
+
+{
+  imports = [
+    (modulesPath + "/installer/cd-dvd/installation-cd-minimal.nix")
+  ];
+
+  environment.systemPackages = with pkgs; [
+    neovim
+  ];
+
+  isoImage.squashfsCompression = "gzip -Xcompression-level 1";
+}