Migrate to labkit errortracker

Migrates us from raven-go to labkit's errortracking module, which in turn is based on the newer sentry-go module.

This also fixes the issue where correlation IDs were not attached to Sentry reports.

I tested this against the sentry-testing project. Sample error report: https://sentry.gitlab.net/gitlab/sentry-testing/issues/2422205/

The way Sentry error tracking, logging, and our helper facades interact with each other is still a bit odd. But we can take it one at a time.