insights: spike issue for migrating away from TimescaleDB

Created by: CristinaBirkel

One of the large remaining items on our roadmap for GA is: https://github.com/sourcegraph/sourcegraph/issues/24430

This spike issue is to front-load the investigation such that we are confident in what the work involves and if there are any big gotchas. After completing this spike issue we should be able to estimate the work and create any sub-tasks that will be needed for it.