Hosts, Use directory-driven hosts in flake.nix

This adds some code to flake.nix to read the directory of hosts/ and
find all hosts based on their host.nix file, and set the hostname based
on the directory.

I don't know enough about hostnames to know what are valid characters,
but in the future this could allow a hostname such as "servers/madoka"
which may be an issue. For now the structure is simple enough of
"hosts/name" resulting in hostname "name"

Another commit is planned which will do the same thing for users

hosts/onizuka/host.nix

@@ -0,0 +1,33 @@
+{ ... }:
+
+{
+  imports = [
+    ./hardware.nix
+  ];
+  networking.hostName = "onizuka";
+  nixpkgs.config.allowUnfree = true;
+  system.stateVersion = "23.05";
+
+  nvidia.enable = true;
+  pipewire.enable = true;
+  polkit.enable = true;
+  tablet.enable = true;
+
+  user.name = "pan";
+  user.timezone = "America/Los_Angeles";
+  system.doAutoUpgrade = true;
+
+  tuigreet.enable = true;
+  hyprland.enable = true;
+
+  librewolf.enable = true;
+  fish.enable = true;
+  fish.setDefault = true;
+  syncthing.enable = true;
+
+  steam.enable = true;
+  steam.gamemode.enable = true;
+  aagl.enable = true;
+  aagl.honkai-rail = true;
+  input-remapper.enable = true;
+}