Adding option to enable window_tabs;

This option, for now, defaults to false. This is just so it keeps the
initial design intention for the original design of the plugin. I may
flip it or change the name of the variable in future commits. This patch
is addressing catppuccin/tmux#16.

Co-Authored-By: Robert Menke <robert.b.menke@gmail.com>

catppuccin.tmux

@@ -16,7 +16,9 @@ get-tmux-option() {
 
 main() {
   local theme
+  local window_tabs_enabled
   theme="$(get-tmux-option "@catppuccin_flavour" "mocha")"
+  window_tabs_enabled="$(get-tmux-option "@catppuccin_window_tabs_enabled" "false")"
   tmux run -b "$CURRENT_DIR/catppuccin-${theme}.tmuxtheme"
 }