"http://" and port number forced on feed xml addresses

[bartlibert]

I have podsync running on my own server behind nginx, with https enabled.
This means it is available at "https://podsync.myserver.net". However, the xml feed contains references to "http://podsync.myserver.net:9090/", which does not work for two reasons: it does not use ssl, which is required on my server + port 9090 is not exposed, the "podsync" subdomain just redirects to it.

[mxpv]

That's the opposite to #43
Probably port and hostname should be independent.
So it'd be possible to cover both cases:

port=8080
hostname=http://myserver:8080

and for cases with frontend

port=8080
hostname=https://myserver.net (nginx redirects to `http://localhost:8080`)

It might also make sense to embed https functionality (for instance with automatic Let's encrypt).

[bartlibert]

This seems a good solution. Maybe make the builtin Let's encrypt support optional, as it might interfere with nginx encryption (not sure?)?

[mxpv]

@bartlibert for sure, it must be optional