Prepare an API behavior document for all the APIs used by the app

[maskaravivek]

Summary:

The commons app uses quite a few MediaWiki APIs throughout the app. It would be great to have an API collection with all the HTTP calls added there.

It would facilitate in debugging issues quickly. We can quickly call and check an API to observe the response/latency or timeouts.

We can probably use https://www.postman.com/ or https://postwoman.io/ or some other framework for our API collection.