feat(ops/deploy-whitby): Add the start of a script to deploy whitby

Add the beginnings of an auto-deploy script for whitby, intended to
be (eventually) suitable for running automatically in a systemd timer.
The current iteration of the script doesn't actually do any deploying,
but instead takes as an argument a revision, creates a new git worktree
in /tmp with that revision checked out, runs a nix-diff of whitby's
system derivation in the running system and at that closure, puts an
html-rendered version of that diff in the public directory used by
deploy.tvl.fyi, and finally sends a message to IRC via irccat with a
link to that HTML page.

Refs: b/110
Change-Id: Id40525567f8845590c909568befd8d00c07a481c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3145
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
Reviewed-by: kn <klemens@posteo.de>

ops/deploy-whitby/default.nix

@@ -0,0 +1,30 @@
+{ pkgs, ... }:
+
+pkgs.stdenv.mkDerivation {
+  name = "deploy-whitby";
+
+  phases = [ "installPhase" "installCheckPhase" ];
+
+  nativeBuildInputs = with pkgs; [
+    makeWrapper
+  ];
+
+  installPhase = ''
+    mkdir -p $out/bin
+    makeWrapper ${./deploy-whitby.sh} $out/bin/deploy-whitby.sh \
+      --prefix PATH : ${with pkgs; lib.makeBinPath [
+        nix-diff
+        ansi2html
+        git
+      ]}
+  '';
+
+  installCheckInputs = with pkgs; [
+    shellcheck
+  ];
+
+  doInstallCheck = true;
+  installCheckPhase = ''
+    shellcheck $out/bin/deploy-whitby.sh
+  '';
+}