Insights: Optimize historical backfill using only changed commits

Created by: coury-clark

Part of #21784 (closed)

This PR introduces an optimizer that will compress the number of historical data frames that need to be queried by polling against an index of commits.

The method of resolving points from the database had to be changed, and for now supports a fixed 6 month span at 2 weeks intervals (similar as before), but will align data points using last observation carried forward.