Add new method deploy_to_modal to DeployableAgent

[gabrielfior]

Modal (https://modal.com/) is an interesting platform for running cron-like jobs, specially in a hackathon setting, and we could add it as an option for deployment as part of the DeployableAgent's toolkit.

To do:
-> Implement new function deploy_to_modal on DeployableAgent
-> Test it (see GH issue modal-labs/modal-client#1879) - it's not trivial to add the method runner.deploy_app to a class, see error in the linked issue