refactor: move last legacy_modules to modules

modules/programs/docker.nix

@@ -0,0 +1,23 @@
+# Enabled when: always
+{
+  username,
+  pkgs,
+  lib,
+  ...
+}: {
+  environment.systemPackages = [
+    pkgs.docker
+    pkgs.docker-compose
+  ];
+
+  virtualisation.docker = {
+    enable = true;
+    enableOnBoot = lib.mkDefault false;
+    storageDriver = "btrfs";
+  };
+  virtualisation.oci-containers = {
+    backend = "docker";
+  };
+
+  users.extraGroups.docker.members = [username];
+}