[Feature]: Replace FAQ fixed documents with a CMS

### Current Behaviour and Context

Currently, FAQ entries are stored in this repository as part of the documentation. This creates overhead to updating these entries, which somewhat defeats the purpose of them.

We created the FAQs as a way to move faster and have some lightweight docs which intentionally weren't linked to the codebase (unlike our full docs, which are designed to be updated alongside the codebase). This setup doesn't really fulfill this.

### Improved Behaviour

We should move our FAQs into a dynamic CMS - I think a custom post type in Vantage probably is a decent spot for this to live. With the new docs system, we can hook this up fairly easily with an Astro <> WP connector.

At the same time, we should change the sidebar navigation to list only the categories, and then the category pages can link out to the FAQs. We could even consider having all the FAQs for a category on a single page similar to AWS' FAQs:

### Additional Info

_No response_