feat: enable nvim-cmp ghost text

nvim/lua/plugins.lua

@@ -148,7 +148,8 @@ return require('packer').startup(function(use)
                             fallback()
                         end
                     end, {"i", "s"})
-                }
+                },
+                experimental = {ghost_text = true}
             })
 
             -- `/` cmdline setup.