feat(configurations)!: flatten down, introduce meta.nix

Flatten down directory structure:
- From: `./hosts/${configuration-type}/${system}/{configuration,deploy}.nix`
-   To: `./hosts/${configuration-type}/{meta,configuration}.nix`
Keep `system` and `deploy-rs` config in `meta.nix`
Update `flake.lock`

hosts/nixos/__template__/hardware-configuration.nix

@@ -0,0 +1,10 @@
+# This is just an example, you should generate yours with nixos-generate-config and put it in here.
+{
+  fileSystems."/" = {
+    device = "/dev/sda1";
+    fsType = "ext4";
+  };
+
+  # Set your system kind (needed for flakes)
+  nixpkgs.hostPlatform = "x86_64-linux";
+}