[Feature] Expose null ls setup to user config (#1323)

* expose null_ls setup to user config

* add new config to example configs

* fix tabs with stylua

* change else statement in the example

lua/default-config.lua

@@ -104,6 +104,9 @@ lvim = {
     on_init_callback = nil,
     ---@usage query the project directory from the language server and use it to set the CWD
     smart_cwd = true,
+    null_ls = {
+      setup = {},
+    },
   },
 
   plugins = {