home: tmux: add 'enabledPassthrough'

This is useful for cases where some programs expect to be able to use
the tmux passthrough escape sequences by using the tmux passthrough
sequence.

One such example is `osc52` script I packaged.

However I like the idea of tmux filtering all escape sequences by
default, so it's not enabled by default.

home/tmux/default.nix

@@ -9,6 +9,8 @@ in
 {
   options.my.home.tmux = with lib; {
     enable = my.mkDisableOption "tmux terminal multiplexer";
+
+    enabledPassthrough = mkEnableOption "tmux DCS passthrough sequence";
   };
 
   config.programs.tmux = lib.mkIf cfg.enable {
@@ -63,6 +65,13 @@ in
 
       # Allow any application to send OSC52 escapes to set the clipboard
       set -s set-clipboard on
+
+      ${
+        lib.optionalString cfg.enabledPassthrough ''
+          # Allow any application to use the tmux DCS for passthrough
+          set -g allow-passthrough on
+        ''
+      }
     '';
   };
 }