Move the API for climate indicators into the climate indicators page, to make reading the api page easier.

[Zeitsperre]

Problem

Loading the API page is a very slow affair when browsing the docs, and this is primarily due to how much content is present within it. The listing for all climate indicators likely doesn't need to be present here when we already have them elsewhere.

[Zeitsperre]

This page has been significantly sped up since adopting the furo theme, with the optional sub-index. Closing.