Make the monthly retention report use a 28 day sliding window
Make the monthly retention report use a 28 day sliding window

acmiyaguchi/data-pipeline,mozilla-services/data-pipeline,acmiyaguchi/data-pipeline,mozilla-services/data-pipeline,mozilla-services/data-pipeline,mozilla-services/data-pipeline,acmiyaguchi/data-pipeline,acmiyaguchi/data-pipeline