chore: [release-3.0.x] fix: codec not initialized in downstream roundtripper

[grafanabot]

Backport b6049f6 from #12873

---

What this PR does / why we need it:
Looks like part of this PR introduced this bug. Root cause is codec is nil (never initialized) and panics during downstream Do.

Above patch, converted QueryFrontend tripperware into middleware but failed to pass the right codec to downstream roundtripper.

This PR passes the codec during InitFrontend.

Which issue(s) this PR fixes:
Fixes #12842

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• For Helm chart changes bump the Helm chart version in production/helm/loki/Chart.yaml and update production/helm/loki/CHANGELOG.md and production/helm/loki/README.md. Example PR
• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR