Add Modal deployment template

[shababo]

This PR adds Modal to the list of deployment templates. Modal relies on a Python/code-centric API for deploying scalable applications in the cloud; therefore this PR includes more than just a single configuration file. Instead it provides a version of the agent-starter-python application which has been modified to run on Modal.

Notes

• only local dependency is modal; other dependencies are defined in the code using a modal.Image
• scaling and container management configuration defined in the app.cls decorator
• memory snapshotting to avoid download-files on every cold-start
• taps into LiveKit via webhooks, in particular the room_started, room_finished, and participant_left events
• local_entrypoint is used to launch pytest on a cloud container

See modal/README.md for more information on using the example app.