How to Add Folders and Files into Master Page Gallery on Modern Team Sites

Sometimes, especially when developing custom SharePoint Add-ins, we want to host assets (JavaScript, CSS, etc.) in Master Page Gallery.
This is a pretty standard approach that allows to reference the same resources from sub sites (I know that sub sites are now evil =)) but store everything in one place on root level of the site collection.
Note: it is not necessary to host your assets in Master Page Gallery, it is one of the options. So, take it in mind, that you can use other options as well. But what if we want to use that approach with Modern Team Sites?