Python: Add observability for MCP tool according to the latest OTel 1.40.0 conventions

[TaoChenOSU]

We should instrument MCP tools according to the latest OTel conventions.

The conventions for MCP tool are documented here: https://github.com/open-telemetry/semantic-conventions/blob/main/docs/gen-ai/mcp.md.

Our observability module is located in: https://github.com/microsoft/agent-framework/blob/main/python/packages/core/agent_framework/observability.py

Tools are defined in: https://github.com/microsoft/agent-framework/blob/main/python/packages/core/agent_framework/_tools.py

MCP tools are defined in: https://github.com/microsoft/agent-framework/blob/main/python/packages/core/agent_framework/_mcp.py