Add a simple Insights support on the server side and a simple api /fetchInsights to fetch them

References #2 (closed)

To test this MR, please check out the fetchInsights HTTP entrypoint, which has several arguments for filtering and sorting the fetched insights. You can use the /api swagger generated UI on a dev build to do some manual tests.

There are two implemented insight detectors/generators: high weekly bounce rate and mail inactivity (code is in the insights directory).

In order to generate some insights quickly, you can change the file workspace/insights.go, change the insights configurations on it and rebuild the application, leaving it running for some time compatible with the configuration you changed (I recommend using values in the range of a few seconds or minutes).