Implement the retrieval/reading of the Insights file to be used in the Insights controller

This is a prerequisite for https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9776.

The following discussion from !9776 (merged) should be addressed:

• @rymai started a discussion:

  We'll need to implement the reading from the real insights.yml file before we can merge this MR! /cc @godfat @markglenfletcher