Move `Use APIs` landing page to a new md file as a subsection

[ronnyhdez]

https://nasa-openscapes.github.io/earthdata-cloud-cookbook/how-tos/use_apis.html

That's the only landing page we have under the how-to's subsections. To continue with the navitagtion pattern we have, it's better to move this landing page as a subsection (same level as AppEEARS Cloud CSV Access