[flake] embrace our new nix overlords tighter (#92)

Why
===
* We didn't install python or poetry last time

What changed
===
* Add python 3.11 and poetry

Test plan
===
* flake built on linux and poetry was workin'

Author: ryantm

flake.nix

@@ -17,7 +17,10 @@
         # Needed for Python/gRPC to be able to interact with libstdc++.
         LD_LIBRARY_PATH = "${pkgs.stdenv.cc.cc.lib}/lib";
       };
-      packages = replitNixDeps;
+      packages = replitNixDeps ++ [
+        pkgs.python311
+        pkgs.poetry
+      ];
     };
   in
   {