pgadmin: make desktop item

This change adds the .desktop file so that pgAdmin shows up in the menu
system of desktop environments (ex. GNOME, XFCE, etc).

Closes #27067

pkgs/applications/misc/pgadmin/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, postgresql, wxGTK, libxml2, libxslt, openssl, zlib }:
+{ stdenv, fetchurl, postgresql, wxGTK, libxml2, libxslt, openssl, zlib, makeDesktopItem }:
 
 stdenv.mkDerivation rec {
   name = "pgadmin3-${version}";
@@ -29,4 +29,21 @@ stdenv.mkDerivation rec {
     maintainers = with maintainers; [ domenkozar wmertens ];
     platforms = platforms.unix;
   };
+
+  postFixup = let
+    desktopItem = makeDesktopItem {
+      name = "pgAdmin";
+      desktopName = "pgAdmin III";
+      genericName = "SQL Administration";
+      exec = "pgadmin3";
+      icon = "pgAdmin3";
+      type = "Application";
+      categories = "Application;Development;";
+      mimeType = "text/html";
+    };
+  in ''
+    mkdir -p $out/share/pixmaps;
+    cp pgadmin/include/images/pgAdmin3.png $out/share/pixmaps/;
+    cp -rv ${desktopItem}/share/applications $out/share/
+  '';
 }