Add get user tool to demo obo flow by referencing Node sample

Add a new tool that gets info of logged in user from Microsoft Graph to demonstrate OBO (on-behalf-of) flow in MCP server. 

Use this Node sample as a reference: https://github.com/anthonychu/mcp-sdk-functions-hosting-node-auth

The goal is to add the new tool and related files to demo the OBO flow. Don't do anything else. Summarize what you've done. 