feat(haystack): auto-instrument Haystack 2.x generators incl. AzureOpenAIChatGenerator; add Azure example + docs

[devin-ai-integration]

📥 Pull Request

📘 Description
Implements full Haystack 2.x auto-instrumentation for AgentOps to resolve the reported issue with AzureOpenAIChatGenerator not being tracked. This adds:

• Auto-instrumentation: New HaystackInstrumentor that wraps OpenAIGenerator and AzureOpenAIChatGenerator methods to capture LLM calls, prompts, and responses
• Azure example: Demonstrates instrumentation with AzureOpenAIChatGenerator including proper validation
• CI integration: Both Haystack examples added to examples integration test workflow
• Updated docs: Added supported generators list and links to both examples

The instrumentor follows existing agentic library patterns, registering as "haystack" in AGENTIC_LIBRARIES to automatically activate when haystack-ai 2.x is imported.

🧪 Testing

• ✅ Pre-commit checks passed locally
• ✅ OpenAI example validated locally: Generated session link showing 2 spans captured with proper token tracking (48 total tokens, $0.0000216 cost)
• ⚠️ Azure example requires manual testing - depends on AZURE_OPENAI_* environment variables (gracefully skips if missing)
• ⚠️ CI workflow not yet triggered - examples integration test workflow hasn't run due to repository settings

⚠️ Human Review Checklist

• Verify instrumentor correctly captures Haystack LLM calls (test with actual haystack-ai package usage)
• Review content extraction logic in _first_non_empty_text() and _extract_prompt() for Haystack data structure compatibility
• Test Azure example with real Azure OpenAI credentials
• Confirm examples run successfully in CI when workflow is enabled
• Validate span attributes align with AgentOps conventions

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Link to Devin run: https://app.devin.ai/sessions/684e8b0399eb48c2b09cf5e9a9b96bf8
Requested by: @areibman

[devin-ai-integration]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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