Registering a custom post type

Inside the code repository, visit wp-content/mu-plugins/post-types-and-taxonomies/post-types.

Create a new file named cpt_something.php. Use one of the examples already in place as a starting point.

Afterwards, go to wp-content/mu-plugins/post-types-and-taxonomies/custom-post-types.php and ensure the custom post type is included.