Migrate all Logs to LabKit v2
This MR flips the switch on the logging setup with gitlab-shell over to LabKit's v2 slog-based package.
For those without the context, we've rolled out a number of pre-cursor MRs to enable us to get to this point. We started by identifying some low-risk log messages, duplicating them and deploying the change to production to verify that these logs were successfully ingested by our system.
We've then incrementally tweaked that setup to try and ensure parity with the current logging setup.
There are 2 MRs that should precede this one:
- !1380 (merged) - migrates all bar gitlab-shell over to the new slog labkit setup
- !1372 (merged) - adopts the latest LabKit log file-writing API
The plan is to land all 3 of these in production with a new version release, then validate that we're haven't introduced any regressions. Given that this service is relatively low traffic, the risk involved in this is somewhat minimal. If we notice any production issues, we can revert the version bump quickly, and it'll revert us back to the last safe state.