control timeout configuration using config/env vars

[risicle]

Doing a few things here to make some of the database tweaks we do and timeouts we set more consistent and controllable via environment variables (which will become useful when we e.g. want to use different statement_timeout values for different daemons.

Replacement for #4218

See commits for individual detail..

Successfully tested on dev-a https://concourse.notify.tools/teams/dev-a/pipelines/deploy-notify/jobs/test/builds/52