Add readme for telemetry guide

[srnagar]

This pull request adds initial documentation for telemetry support in the Azure MCP Server. The new TELEMETRY_README.md provides an overview of telemetry architecture, configuration, collected data, and privacy considerations for different versions of the server, with a focus on recent enhancements for user-provided Application Insights integration.

Documentation additions:

• Added a comprehensive telemetry guide (TELEMETRY_README.md) covering telemetry architecture, configuration via environment variables, and feature differences between versions 2.0.0-beta.5 and 2.0.0-beta.6+
• Documented new HTTP trace instrumentation and smart filtering features available in version 2.0.0-beta.6+ for self-hosted HTTP mode scenarios
• Provided detailed instructions for enabling/disabling telemetry and troubleshooting common issues
• Outlined privacy principles, types of data collected, and future documentation plans