Allow extending auto-imports config

**Is your feature request related to a problem? Please describe.**

As far as I'm aware, there's no way to extend the auto-import functions used by iles.

It would be useful for devs as they could auto-import from specific folders easily (e.g Nuxt auto-imports composables dir), as well as module authors who can register auto-imported functions.

**Describe the solution you'd like**

A config similar to `components` which can easily be extended

**Describe alternatives you've considered**

Don't mind the implementation

**Additional context**
Add any other context or screenshots about the feature request here.