chore: add dependency to kerberos MCP-89

[kmruiz]

This is necessary for clients that can use kerberos. It's registered as an optional dependency so clients that can't use kerberos because they don't have the required system dependencies can still use the MCP Server w/o kerberos support.

Proposed changes

Checklist

• I have signed the MongoDB CLA

[Copilot]

Pull Request Overview

This PR adds Kerberos authentication support to the MCP Server by including the kerberos package as an optional dependency. This allows clients with the necessary system dependencies to utilize Kerberos authentication while ensuring the server remains functional for clients without Kerberos support.

• Adds kerberos as an optional dependency to enable authentication for compatible clients
• Maintains backward compatibility for environments without Kerberos system dependencies

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[nirinchev]

Is there anything we should do to handle the case where kerberos cannot be installed or will the error messages of trying to use kerberos auth bubble up nicely? If it works automagically, then let's 🚢 🇮🇹

[kmruiz]

We already show a decent error message when we can't load kerberos :D that says that kerberos is not available and the system error (that comes from Kerberos itself): https://github.com/mongodb-js/mongosh/blob/main/packages/service-provider-node-driver/src/node-driver-service-provider.ts#L372C11-L374C14