Add AgentGateway integration guide under gateway for LLM observability via OpenTelemetry

[ProfessorSeb]

Adds a new integration guide for AgentGateway (https://agentgateway.dev/) under the Gateways section.

What's covered:

• Architecture overview: AgentGateway → OTEL Collector → Langfuse pipeline
• Step-by-step OTEL Collector deployment with Langfuse otlphttp exporter
• Tracing configuration for both Enterprise and OSS editions
• Rich GenAI semantic conventions (model, token usage, prompt/completion, HTTP context)
• LLM backend + HTTPRoute setup example (OpenAI)
• Advanced: multiple exporter fanout, metadata/header forwarding for user/session tracking
• Troubleshooting table

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Important

Adds an integration guide for AgentGateway with Langfuse using OpenTelemetry, covering architecture, deployment, configuration, and advanced features.

• Integration Guide:
  • New agentgateway.mdx file under pages/integrations/gateways/.
  • Covers integration of AgentGateway with Langfuse using OpenTelemetry.
• Architecture & Deployment:
  • Describes architecture: AgentGateway → OTEL Collector → Langfuse.
  • Step-by-step OTEL Collector deployment with Langfuse otlphttp exporter.
• Configuration:
  • Tracing configuration for Enterprise and OSS editions.
  • Rich GenAI semantic conventions for model, token usage, etc.
• Advanced Features:
  • Multiple exporter fanout and metadata/header forwarding for user/session tracking.
• Troubleshooting:
  • Includes a troubleshooting table for common issues.

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