Consider using custom `user.config`

[Iordanis Petkakis]

I'm not sure if the current implementation supports it or not, but it would be worth considering that a user with a custom configuration not based on any Neovim distro, might have a different file structure, such as:

├── lua
│   ├── autocommands.lua
│   ├── keybindings.lua
│   ├── plugins
│   │   ├── animate.lua
│   │   ├── completion.lua
│   │   └── editor.lua
│   └── settings.lua

It would be useful, for any user with a custom configuration close to the file architecture as stated above, to be able to customize his user.config with the filenames provided by his own choosing. Not sure if this needs special implementation or if we could provide just an extra example in the Adding custom presets to show how such a thing can be achieved with return_spec method.