lineage events: add endpoint to filter events by namespace

[mobuchowski]

There should be endpoint that allows you to search for events relating to particular namespace - meaning either job namespace, or dataset namespace. We couldn't do it before, because it would mean full scan of lineage_events table. Since adding dataset_facets tables, we can implement it efficiently.

As a future work, we should consider allowing filtering only by one of those, meaning only events that rely to particular dataset namespace, or job namespace.