Ignorable path parts / shadowed folder names

[Mahfoudh94]

Summary

Influenced by routing in Next.js, we need a way to group elements like having a page in src/pages/(markets)/home.astro corresponds to https://example.com/home (the (market) in the path was ignored), this would allow for easier grouping, especially for content generation

Background & Motivation

The main source of the idea is next.js and some routing solutions for front-end frameworks
I felt the need for it in the content generation for SSG sites, optimized for speed and load time

[austinm911]

duplicate of #480, you should go ahead and upvote that one as well