Loki 3.7.1 upstream has a regression which does not allow tracing

[sinapah]

We moved to Loki version 3.7.1 in #44. To enable tracing, we will revert back to 3.6.7, which was the version used before we moved to 3.7.1. Once the upstream issue grafana/loki#21588 is resolved, we can reconsider moving to that version.