[WIP] Charm logging tracing integration

[PietroPasotti]

based upon #392

Logs --> traces

If a charm is using charm_tracing and charm_logging (and both are active and healthy), we should be able to link traces and logs generated by each charm execution.

This PR links logs to traces by:

• tagging all logs with the trace ID obtained from the context
• configuring the loki datasource to link each log tagged with a trace ID to the appropriate tempo trace in grafana

Open questions/challenges

• the charm_logging decorator needs to be applied before the charm_tracing one, otherwise logging will be unaware of the tracing context and fail to acknowledge the root span id.

Resources:
https://grafana.com/docs/grafana/latest/datasources/loki/#provision-the-data-source