postgresql: Fix use with extensions

Fixes #15512 and #16032

With the multi output, postgresql cannot find at runtime what is its
basedir when looking for libdir and pkglibdir. This commit fixes that.

nixos/modules/services/databases/postgresql.nix

@@ -11,12 +11,14 @@ let
     if cfg.extraPlugins == [] then pg
     else pkgs.buildEnv {
       name = "postgresql-and-plugins-${(builtins.parseDrvName pg.name).version}";
-      paths = [ pg ] ++ cfg.extraPlugins;
+      paths = [ pg pg.lib ] ++ cfg.extraPlugins;
+      buildInputs = [ pkgs.makeWrapper ];
       postBuild =
         ''
           mkdir -p $out/bin
           rm $out/bin/{pg_config,postgres,pg_ctl}
           cp --target-directory=$out/bin ${pg}/bin/{postgres,pg_config,pg_ctl}
+          wrapProgram $out/bin/postgres --set NIX_PGLIBDIR $out/lib
         '';
     };