Generate archetype docs

[teh-cmc]

We require 3 different kinds of docs for our archetypes:

• Native language docs (docstrings)
  This is automatically handled by codegen already.
• Doc reference
  We need to completely overhaul this for the new type-based APIs, and as much as possible automate it via codegen or it's going to be out-of-sync very fast.
• High-level example page (doesn't exist yet!)
  Needs to show a thumbnail for all archetypes and link to the reference.

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API references are already taken care of by the language-specific codegen backends, but we still need a codegen backend that takes IDL definitions in and turn them into documentation for the website (e.g. all the archetype related pages).

Contents of:
docs/content/reference/data_types

[emilk]

Related: the doc-examples should be auto-included. No need to add manual \cpp ## Example to all our archetypes imho.

That way we will also catch any missing doc-examples