I'd like to create a new page in the wp-admin panel. I know I should use the
add_menu_page() function for that and I understand how it works.
I'm new to WP development, and would just like to know in which file I should put this function. The doc does not answer to my question, or I don't understand it.
I don't know if it's possible but I'd like this page to be part of neither the plugins nor the themes.
Thanks for your help