insights: timestamp of recorded historical value does not align with the time of the revision

Created by: coury-clark

When data frames are constructed for a backfill, a date is selected that falls in the middle of the interval. This date is used to try and find a commit "closest" to this time. However, when the point is actually resolved - the time is not extracted from the commit. This causes a slight mismatch between the recordings and the actual committed time.

https://sourcegraph.com/github.com/sourcegraph/sourcegraph@main/-/blob/enterprise/internal/insights/background/historical_enqueuer.go?L422 https://sourcegraph.com/github.com/sourcegraph/sourcegraph@main/-/blob/enterprise/internal/insights/background/historical_enqueuer.go?L481