docs: create comprehensive telemetry guide (telemetry.md) #93

Summary

Created docs/telemetry.md — a comprehensive OpenTelemetry guide for AgentOps evaluation tracing.

What was done

New document covering:

• Why Telemetry — motivation and goals
• Concepts — OTel primer (traces, spans, exporters)
• How AgentOps Uses OTel — lazy init, env-var activation
• Quick Start — 3-step Jaeger setup with Docker
• Environment Variables — AGENTOPS_OTLP_ENDPOINT, AGENTOPS_OTLP_HEADERS, OTEL_SERVICE_NAME
• Trace Tree — visual span hierarchy
• Semantic Conventions — three layers (CICD, GenAI, AgentOps) with full attribute tables
• Viewing Traces in Jaeger — screenshots guidance
• Sending Traces to Azure Monitor — OTLP ingestion config
• Evaluation Tracing vs Agent Execution Tracing — comparison table clarifying what AgentOps traces vs what Foundry/Agent Framework traces
• FAQ — common questions

Implemented in

PR #86 (feature/telemetry-doc -> develop)