Add support for VS Code's Azure DevOps Codespaces Auth extension

[scaryrawr]

This is a follow up of #527 .

When using Visual Studio Code with GitHub Codespaces connected to Azure DevOps, the ADO Codespaces Auth Extension adds a helper script called ado-auth-helper in the user's home directory.

This ado-auth-helper script can be called to get an access token to Azure DevOps with the default scope by calling ~/ado-auth-helper get-access-token.

The script does some routing through VS Code to have it handle authentication (so users in GitHub Codespaces do not need to do device auth when using this extension).

The limitation of this script is it doesn't support tenant specific authentication (though it is configurable in the extension's settings).

Auto detecting this script and use in Codespace would make it easier on users since they would not have to configure the Azure CLI.

[aaudzei]

If my understanding is correct the suggestion is to use ADO Codespaces Auth Extension as an ADO token provider for MCP server API calls.

In general this sounds like a good idea. But first we need to evaluate if the OAuth client behind vscode.authentication is preauthorized to the OAuth scopes necessary for MCP server operations by ADO resource identity. Gut feeling is that it is only limited to "git operations".

Suggested create Codespaces with the extension. Use terminal to execute ~/ado-auth-helper get-access-token, check JWT claims and Entra confiration of ADO preauthorizations.

If the auth token is proved to be sufficient then the Codespaces startup script can be extended to recognize presence of extension, execute it and store resulting token in env to be used by MCP server via --authentication env startup param