Lobby: add support for HTTPs

[Indy2222]

• Document appropriate way how to enable HTTPS on the server side (directly from the server vs nginx and similar "proxies" e.g. in K8s).
• Add direct support for HTTPS to Lobby server (via rust-tls).
• Support HTTPS (and enforce signed certificates) to the client.
• Enforce HTTPS unless HTTP is enabled (opt-in) in the configuration.