feat(3p/josh): Import and build josh

We've had josh in here previously, but it was kind of immature back
then. The repository looks much better now and I'd like to give it
another try.

Josh is a Rust project, the build here is done with naersk.

Change-Id: I3731340d00ce1eb4cef55de114e1915579e47ef3
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3017
Reviewed-by: lukegb <lukegb@tvl.fyi>
Tested-by: BuildkiteCI

third_party/josh/default.nix

@@ -0,0 +1,33 @@
+# https://github.com/esrlabs/josh
+{ depot, pkgs, ... }:
+
+let
+  gitSrc = pkgs.fetchFromGitHub {
+    owner = "esrlabs";
+    repo = "josh";
+    rev = "1c1965deb0278de92452a597c092f16b531274ae";
+    sha256 = "0a0ybx4dqr9gfcn1kqy2nirdsfbdwkfz24ljnri564c5381ccldw";
+  };
+
+  src = pkgs.applyPatches {
+    name = "josh-src";
+    src = gitSrc;
+    patches = [
+      ./pin-git2-rev.patch
+    ];
+  };
+in depot.third_party.naersk.buildPackage {
+  inherit src;
+
+  buildInputs = with pkgs; [
+    libgit2
+    openssl
+    pkgconfig
+  ];
+
+  cargoBuildOptions = x: x ++ [
+    "-p" "josh"
+    "-p" "josh-proxy"
+    "-p" "josh-ui"
+  ];
+}