Customizing module types initialization outdated

**Your Godot version:** stable (4.x)

**Issue description:**

**URL to the documentation page:** https://docs.godotengine.org/en/stable/contributing/development/core_and_modules/custom_modules_in_cpp.html#customizing-module-types-initialization

The `preregister_{module_name}_types()` does not work anymore. Instead probably `if (p_level == MODULE_INITIALIZATION_LEVEL_CORE)` inside of the `initialize_{module_name}_module()` should be used.

It would be awesome to have some documentation about when to use what value from the `ModuleInitializationLevel` enum.
This then also could be referenced in https://docs.godotengine.org/en/stable/classes/class_gdextension.html or vice versa.