Basic Feature // Allow folders to be created, with nesting directories in collections

This is somewhat related to the unsolved #3591 which was posted back in 2022, but I don't think that's going to be addressed.

An example of a very useful basic feature to implement is allowing folders to be nested inside collections. I think it's self-explanatory - this allows for efficient organization and subcategorizing without the need to make additional collections.

Edit: For context, yesterday, I set up a self-hosted instance. It was a nightmare to set up, taking me four hours _with assistance,_ and after all of that, I was horrified to see that I couldn't even create subdirectories for the archive I was planning to create. I would consider this a crucial and highly warranted feature. I want to be able to use Outline for my project.