Add Observability Fundamentals section to the repository

The repository already provides excellent coverage of distributed systems and system design concepts. However, observability-related topics are currently either partially covered or scattered across different sections.

Suggested Improvement

Add a dedicated Observability Fundamentals section containing resources related to:

Metrics Logging Monitoring Distributed Tracing OpenTelemetry basics Alerting strategies Why this would help Observability is a core part of modern distributed systems and backend engineering. It helps learners understand how production systems are monitored and debugged. It improves the repository’s completeness for system design interviews and real-world engineering concepts. Possible Resources Prometheus Grafana OpenTelemetry Distributed tracing articles RED/USE monitoring methodologies

I would be happy to contribute relevant high-quality resources if this enhancement is approved.