build(nix): add dependencies for launching GUI client (#9135)

In order to launch a debug build of the GUI client on NixOS, we need to
add the appindicator dependency and set the library lookup path
correctly.

scripts/nix/flake.nix

@@ -48,6 +48,7 @@
         pango
         webkitgtk_4_1
         webkitgtk_4_1.dev
+        libayatana-appindicator
       ];
     in
     {
@@ -58,6 +59,7 @@
           src = ../..;
 
           PKG_CONFIG_PATH = with pkgs; "${glib.dev}/lib/pkgconfig:${libsoup_3.dev}/lib/pkgconfig:${webkitgtk_4_1.dev}/lib/pkgconfig:${at-spi2-atk.dev}/lib/pkgconfig:${gtk3.dev}/lib/pkgconfig:${gdk-pixbuf.dev}/lib/pkgconfig:${cairo.dev}/lib/pkgconfig:${pango.dev}/lib/pkgconfig:${harfbuzz.dev}/lib/pkgconfig";
+          LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath [ pkgs.libayatana-appindicator pkgs.gtk3 pkgs.glib ];
         };
       };
     };