docs: add OpenTelemetry GenAI instrumentation sample

[dineshkumarkummara]

Motivation and Context

Currently, Semantic Kernel does not ship an example of how to adopt the new OpenTelemetry GenAI semantic conventions.
This makes it difficult for developers to instrument SK-based applications with end-to-end observability (latency, token usage, error rates, tool-call spans, and retrieval latency).

This PR contributes a documentation/sample entry showing how to instrument SK with OpenTelemetry using the SkOtel library.
The goal is to provide the community with a ready-to-run reference that aligns with the OTel GenAI spec.

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Description

• Adds a docs page under samples/ demonstrating OTel GenAI instrumentation for SK.
• Shows how to register AddSemanticKernelTelemetry middleware and a DelegatingHandler.
• Provides runnable example (sk-chat) plus Dockerized Collector → Tempo → Prometheus → Grafana stack.
• Includes screenshot of a Grafana token throughput panel to illustrate expected telemetry output.

This contribution is docs/sample only — no changes are made to SK core runtime code.

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Contribution Checklist

• The docs build clean without any errors or warnings
• The sample code runs successfully and emits OTel telemetry
• The PR follows the SK Contribution Guidelines
• Screenshots and snippets are verified against the live repo example
• This is a docs/sample addition — no breaking changes introduced

[dineshkumarkummara]

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[dineshkumarkummara]

Hi, this is a docs/sample contribution showing how to enable OpenTelemetry GenAI instrumentation in SK. All docs build locally. Looking forward to your feedback.