TLS-based message transport

[c42f]

It might be cool to have a RemoteREPL transport option to use TLS. Then

• It would be possible to expose the RemoteREPL port directly over the internet
• RemoteREPL users can benefit from the existing TLS public key infrastructure
• But with an open port we'd need to include a password or authentication token of some kind before accepting any connection.

Perhaps it could make sense to just use https to frame messages and eventually benefit from cool things like HTTP/3 and QUIC. However RemoteREPL is currently more suited to a stream based transport rather than request-response as it will let us do things like incrementally push logs back to the client and perhaps multiplex other Julia streams (eg proxies for stdin and stdout?) over the connection.