Last active time mismatched between new and deprecated usage stats libraries

Created by: dadlerj

Reported by https://app.hubspot.com/contacts/2762526/company/557691596

We're in an odd state where the list of users that appear on the site-admin/usage-statistics page is populated by querying both the new (postgres-based) and the old (redis-based) usage stats libraries.

The former is used to generate the list of users who have been active "in the current day, week, month", while the latter is used for actually listing their activity details (searches, page views, last active time).

A user reported that someone appeared on the usage statistics page when filtered by "Active today", that had a "last active date" of "yesterday". This is reproducible on sourcegraph.com, but I'm having trouble doing so locally.

https://github.com/sourcegraph/sourcegraph/pull/9141 will allow me to audit the former usage stats library (i.e., the new one), which is critical to this investigation.