More precisely, check if we can call set_webhook automatically in more cases. Things to consider:

1. As of API 5.0 we have the drop_pending_updates parameter, so we can handle the clean logic more elegantly
2. SSL-settings can be applicable at two different "positions": the URL where TG sends the updates to and the webhookserver, where we fetch them. those two are not necessarily the same (e.g. reverse proxy)
3. citing jannes: "I think we could use the cert to set the webhook if available, but only use it for SSL termination if there is also a key provided" (which needs to be double checked)