for those who might want to test this PR, here is a way to add a config report with a diff view (as generated by puppet for example):

download the attached report.json and execute

curl -ku admin:changeme -H 'Content-Type: application/json' http://localhost:3000/api/config_reports -d @report.json -v -X POST

Applied in changeset dbb57cc3aea6e454253a4d33de1d6b79743d41d3.