Motivation and Context

SK has included the OTel semantic conventions as an experimental feature.

Description

This PR updates the telemetry sample app to show case the feature and removes the use of planners in the sample app as not all connectors work with the Handlebars planner (The Handlebars planner has multiple system messages, but the Gemini connector doesn't allow that).

This PR also updates the documentations for telemetry.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄