feat(tazjin/tgsa): Implement initial tg embed -> BBcode features

Supports only posts with plain photos, and loses all message
formatting, but it's getting there.

Change-Id: I9e4afcf3072d1e0724521ccbdc1338fe4f8d5ebe
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5466
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

users/tazjin/tgsa/default.nix

@@ -0,0 +1,10 @@
+{ depot, pkgs, ... }:
+
+depot.third_party.naersk.buildPackage {
+  src = ./.;
+
+  buildInputs = with pkgs; [
+    pkgconfig
+    openssl
+  ];
+}