Add options for enabling tls in frontend and backend

[grs]

[ssorj]

Thanks, Gordon! Use of Uvicorn and HTTPX is incidental, and I'd like more generic option names. Would you be happy with these:

--tls-cert <cert-file>       Default: none
--tls-key <key-file>         Default: [value of --tls-cert]
--tls-trust <cert-file>      Default: [system-default CAs]
--tls-verify <boolean>       Default: false

I'd be happy to make those changes on top of yours, if you agree.

[grs]

Yes, makes sense to me.