Overview pages

## nit

I like API reference pages. They provide good CTR and overview for the user. Example on current telefunc proto docs:
https://richard-unterberg.github.io/vike-docpress/api/

Therefore a new Component was created for usage in mdx / tsx files:

```ts

```

this will spawn a responsive 2/x grid with the resolved values from the [headings.ts](https://github.com/richard-unterberg/vike-docpress/blob/master/packages/telefunc/lib/headings.ts)

WDYT @brillout

Start with the proposed usage in the issue and inspect the linked headings.ts file to understand how heading keys resolve. Clarify the intended scope and placement in docpress before implementing; done means the component renders the requested overview content in a responsive two-column grid.

Written by the indexing model from the issue text.