Docs: Hide legacy endpoints and document upcoming ones

[birkjernstrom]

We have a lot of endpoints and many of more internal nature. Let's hide them to focus on the endpoints that will power the use cases we believe are of interest.

Endpoints/cases to focus on

• OAuth & Gatekeeping
• Newsletter Subscriptions (embed/signup subscribers)
• Products (Subscriptions & Products)
• Benefit Grants
• Articles/Newsletters

Separately we can create a page for "Changelog" & "In progress" and in the latter we can communicate that the issue funding endpoints and others are still TBD to be ported over to our new form of API, but that we invite developers to join our Discord if they want to integrate them specifically.

[frankie567]

First part re: hierarchize endpoints done ✅

The doc page about hidden endpoints is still to do