Add method to get most viewed authors from GA

Want a way to get most viewed authors in the past e.g. week from google analytics.

Describe the problem that you'd like solved

Having a way to query google analytics from openlibrary repo would be super useful in letting us show "trending" data. As a basic first step, let's get trending authors.

Proposal & Constraints

• Cache aggressively; like maybe daily? Maybe weekly?
• Will need to GA API keys to production environments

Additional context

• https://developers.google.com/analytics/devguides/reporting/core/v4/quickstart/service-py

Stakeholders