refactor(tools): switch to Nix

- Nix is more reproducible (pinned to a specific hash)
- Faster rebuild after changing the package list (due to /nix caching in volume)
- Users can still use make tools (wrapped in Docker) without installing Nix
- Using nix-shell will work if you have nix installed.

shell.nix

@@ -0,0 +1,40 @@
+# https://status.nixos.org
+{ pkgs ? import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/f034b5693a26625f56068af983ed7727a60b5f8b.tar.gz") {} }:
+
+let
+  python-packages = pkgs.python3.withPackages (p: with p; [
+    jinja2
+    kubernetes
+    netaddr
+    rich
+  ]);
+in
+pkgs.mkShell {
+  buildInputs = with pkgs; [
+    ansible
+    ansible-lint
+    bmake
+    diffutils
+    docker
+    docker-compose_1 # TODO upgrade to version 2
+    git
+    go
+    grc
+    iproute2
+    k9s
+    kube3d
+    kubectl
+    kubernetes-helm
+    kustomize
+    libisoburn
+    neovim
+    openssh
+    p7zip
+    pre-commit
+    shellcheck
+    terraform
+    yamllint
+
+    python-packages
+  ];
+}