home-manager: add force option for gtk-2 config (#7073)

This adds gtk.gtk2.force enable option which maps directly onto home.files.${cfg2.configLocation}.force to allow overwrite of the gtkrc-2.0 file (workaround for bug #6188).

(cherry picked from commit d3f5d870e3)

modules/misc/gtk.nix

@@ -169,6 +169,8 @@ in
             The location to put the GTK configuration file.
           '';
         };
+
+        force = lib.mkEnableOption "GTK 2 config force overwrite without creating a backup";
       };
 
       gtk3 = {
@@ -294,10 +296,14 @@ in
         cfg.cursorTheme
       ];
 
-      home.file.${cfg2.configLocation}.text =
-        lib.concatMapStrings (l: l + "\n") (lib.mapAttrsToList formatGtk2Option gtkIni)
-        + cfg2.extraConfig
-        + "\n";
+      home.file.${cfg2.configLocation} = {
+        text =
+          lib.concatMapStrings (l: l + "\n") (lib.mapAttrsToList formatGtk2Option gtkIni)
+          + cfg2.extraConfig
+          + "\n";
+
+        inherit (cfg2) force;
+      };
 
       home.sessionVariables.GTK2_RC_FILES = cfg2.configLocation;