Swap codeinsights-db docker image to be based off postgres instead of Timescale

Created by: caugustus-sourcegraph

Switches the base for codeinsights-db to Postgres, away from Timescale. This swap preserves the existing postgres uid used by the container, to avoid requiring users to migrate file permissions.

Test plan

Build all three images (postgres, codeintel, codeinsights) and confirm uid assignments are still correct. Confirm codeinsights successfully starts with new image.