rootio/cmd/root-srv: add https+letsencrypt support
Created by: mughetto
PR solving #64 (closed).
Few additional features to (maybe) add during review process:
- Redirect http traffic to https (WIP)
- Sanity check on flags (enforce only 2 possible values for serv flag (http/https), check that CA domain name is given for the https case)
- Do we want a single server instance to serve both http and https requests? (if even possible)