Ensure secure connection (HTTPS) to Argilla

[jmargutt]

We need to ensure that users can connect with HTTPS to Argilla. We need to use nginx to route traffic from public 80 to local port. Then SSL can be setup on nginx easily using letsencrypt certbot. Ideally, all should be configured in the docker-compose.yaml file for easier re-deployment.

• Update docker-compose.yaml accordingly, working this branch argilla-sml/nginx
• Deploy and test on sml-argilla-prod. N.B. despite the name, it does not contain production data, so don't worry about breaking things.
• Update documentation, if necessary