bitdynamics-ab/canton-devkit: docs/observability.md

# Observability — Prometheus + Grafana The `--profile observability` flag on `canton-devkit localnet up` adds two containers to the compose project: - **Prometheus** scrapes `canton:10013` and `splice:10013` (both containers ship `/app/monitoring.conf` enabling the built-in OTel reporter — see `asse