doom: Add another shortcut for M-x

C-SPC SPC is more convenient on GPD micro because lack of right hand M/C
keys make these shortcuts fairly painful

modules/emacs/doom/config.org

@@ -355,6 +355,8 @@ Customize Modus-themes a little to make it more peppy and vibrant.
 (use-package! emacs
   :config
   (map! :leader
+        :desc "M-x"
+        :g "SPC" #'execute-extended-command
         (:desc "Enlarge window"
          :prefix "w"
          :g "o" #'doom/window-enlargen)