tracing overlay

[PietroPasotti]

added tracing overlay file

• do we need to add anything to the readme/documentation?
• test the overlay

Testing instructions

Deploy the testing and tracing overlay:

tox -e render-edge
juju deploy ./bundle.yaml --trust \
  --overlay overlays/tracing-overlay.yaml \
  --overlay overlays/testing-overlay.yaml

Then, sync latest v2 tracing lib

jhack sync "*" --source-dirs ./lib/charms/tempo_k8s/v2/

Check grafana dashboard that tempo source has charm traces from (alertmanager, prometheus, loki, grafana, tempo, traefik, catalogue)

Add tls overlay:

juju deploy ./bundle.yaml --trust \
  --overlay overlays/tls-overlay.yaml \
  --overlay overlays/testing-overlay.yaml

verify you can still see the new charm traces for all apps (and grafana workload)