repo-updater: refactor logging to use structured lib/log

Created by: bobheadxi

repo-updater does a lot of things, runs pretty async, and it makes asking for log entries for this service rather unhelpful - most log entries only log events with no way to trace entries correlated to a process/event/job. It is a good candidate for migrating to our new logging (https://github.com/sourcegraph/sourcegraph/issues/33192, https://docs.sourcegraph.com/dev/how-to/add_and_use_logging)

Plan: I will pair with new DevX hire starting May on walking through repo-updater, and the (at least partial) migration will be an onboarding task