feat(flake)!: *dogfood* on all flake modules

Export all `./nix/` flake modules
Modularize `configurations` on `machines` dir
Also move `toposort` images to a single attrset binding

modules/flake/agenix.nix

@@ -0,0 +1,13 @@
+{ lib, config, self, inputs, ... }:
+
+{
+  imports = [
+    inputs.agenix-rekey.flakeModule
+  ];
+
+  perSystem = {
+    agenix-rekey = {
+      nodes = self.nixosConfigurations;
+    };
+  };
+}