APIs for new MDN Observatory

[scarytom]

Our automated checks that rely on the MDN Observatory APIs all started failing last week.

I believe this is related to the migration of the Mozilla Observatory to the new MDN observatory. There might be a new API endpoint to use, but I'm not sure. The MDN documentation is pretty unhelpful regarding the migration of APIs.

Please can you at least clarify the situation, and perhaps update the documentation here to help us out.

[argl]

Please see mozilla/observatory-cli#52