leverage content as data for the header component navigation content

[thescientist13]

Summary

Once #84 lands, the initial seeds for content as data will be available (via patch package patches), which means we can now leverage this in the header to generate the navigation menus.

With this, we should also be able to add an "active" class to each navigation item to give it an underline when it is the active page.

Details

Basically we would want to add collection and order to the frontmatter of each of the relevant pages, once they have been done / merged

1. Docs Page #31
2. Guides Page #33
3. Blog Landing Page #34

----
collection: nav
order: 1
----

You can see an example here -

www.greenwoodjs.dev/src/components/header/header.js

Line 16 in 89a6371

const nav = JSON.parse(this.getAttribute("nav") || "[]").sort((a, b) =>

---

We might also want to make it so that the active link gets a style for it, at minumum an underline would be nice, especially when you're on the Docs or Guides pages, since they have similar layouts so having that visual breadcrumb would be nice.