Feat: Operator dash - Add duplicate row counts card

[bmtcril]

We should have a card that checks for duplicate rows, alerting operators that there are duplicates in the tables that may need to be dealt with.

[Ian2012]

@bmtcril do you think this query would work on that one?

SELECT event_id, count(event_id) as counts
FROM xapi_events_all_parsed
GROUP BY event_id
HAVING counts > 1

Or, an MV would be better for that one?

[bmtcril]

This one is going to be tricky, I don't think we can do any kind of direct unbounded aggregation on xapi_events_all_parsed / xapi_events_all due to the size. That query takes ~250 secs on the 1.1B row test db, I tried a few others and they all were around there or worse. You might want to try a pre-aggregated projection on the table that just selects event id and count. If you come up with one that works I can try it on the big dataset and see how it performs.