Introduce ADR on structured logging

docs/adr/002-use-structured-logging.md

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+---
+slug: 2
+title: |
+  2. Use simple structured logging
+authors: []
+tags: [Draft]
+---
+
+## Status
+
+**Draft**
+
+## Context
+
+* Logs are a critical tool for operating any software system, enabling [observability](https://cloud.google.com/architecture/devops/devops-measurement-monitoring-and-observability) of the system.
+* Following [12 Factor Apps](https://12factor.net/logs) principles, providing the needed components and tools to be able to configure logging and monitoring should not be the responsibility of the software components
+
+## Decision
+
+_Therefore_
+
+* Each component of the system use [Structured logging](https://www.sumologic.com/glossary/structured-logging/) using documented and standardised JSON format for its logs
+* Logs are always emitted to `stdout` of the process the component is part of
+
+## Consequences
+
+* The schema of the logged items should be properly documented in a JSON schema
+* It is the responsibility of the node operator to consume the logs and process them
+* We use existing libraries to provide needed log infrastructure, like [slog](https://zsiciarz.github.io/24daysofrust/book/vol2/day4.html) for Rust