add url, agent name, and sandboxid as query params

[tinalenguyen]

this should allow links that users may click for a demo that wouldn't require livekit cloud credentials

[theomonnom]

This should be using any sandboxTokenServer.

I think the simple implementation is to create a new API (Don't reuse src/pages/api/token.ts).

Let's create a new api/examples_token.ts that reads API keys from the configured examples project and generates tokens directly for that project. The agent_name can be passed as a query parameter.