Update 404 detection logic to propagate `broken` status to Data Sources App

[maxachis]

After we finish #338 and bring URLs from data sources into source collector, we'll need to ensure that any broken links we find in our Source Collector logic is propagated back into Data Sources.

With that in mind, when we detect a URL that is broken in Source Collector, we should send that information back to Data Sources indicating which URL is broken. Even better if we can do it in a batch format.