deneb: add default_thai_company frappe app to poyerp

Package git.b4l.co.th/newedge/default_thai_company as a frappix app
    (pkgs/frappix/default-thai-company.nix) and expose it through a new
    frappixAppsOverlay that extends the pkgs.frappix scope. Install it on
    the poyerp.newedge.house site on deneb.

overlays/default.nix

@@ -7,5 +7,6 @@
     frappixLibsOverlay = inputs.frappix.libsOverlay.x86_64-linux;
     frappixPythonOverlay = inputs.frappix.pythonOverlay.x86_64-linux;
     frappixToolsOverlay = inputs.frappix.toolsOverlay.x86_64-linux;
+    frappixAppsOverlay = import ../pkgs/frappix/overlay.nix;
   };
 }