As discussed in #4969, I would like to see nested collections work with the flat content structure.

Currently, nested collections work with only one type of content structure, where every markdown file has to be in its own folder:

content
└── pages
    ├── authors
    │   ├── author-1
    │   │   └── index.md
    │   └── index.md
    ├── index.md

I would like to see it work also with a flatter structure, like this one:

content
└── pages
    ├── authors
    │   ├── author-1.md
    │   └── index.md
    ├── index.md