Support multiple TLS certificates for multiple domains

Currently, copyparty seems to work with a single TLS certificate for HTTPS. I found no built-in way to serve multiple domains with separate certificates without relying on third-party reverse proxies.

I propose adding an option to configure multiple TLS certificates depending on the requested domain. This would allow copyparty to directly handle HTTPS for multiple domains securely, similar to how lighttpd or Nginx can select certificates per host.

For reference, here is how it looks in lighttpd:
```
$SERVER["socket"] == ":443" {
ssl.engine = "enable"
ssl.pemfile = "/etc/letsencrypt/live/mydomain.io/fullchain.pem"
ssl.privkey = "/etc/letsencrypt/live/mydomain.io/privkey.pem"

$HTTP["host"] == "mydomain.com" {
ssl.pemfile = "/etc/letsencrypt/live/mydomain.com/fullchain.pem"
ssl.privkey = "/etc/letsencrypt/live/mydomain.com/privkey.pem"
}

$HTTP["host"] == "mydomain.org" {
ssl.pemfile = "/etc/letsencrypt/live/mydomain.org/fullchain.pem"
ssl.privkey = "/etc/letsencrypt/live/mydomain.org/privkey.pem"
}
}

```
In lighttpd, there should be one default value, so mydomain.io is not under conditions, ignore that.
If this is already possible in copyparty, please let me know how to configure it.