1611: Adds own server on port 80 for letsencrypt and redirect r=mergify[bot] a=elektro-wolle
## What type of PR?
Bugfix
## What does this PR do?
Handle letsencrypt route to `.well-known` by own server configuration within nginx.
### Related issue(s)
closes#1564
## Prerequistes
Before we can consider review and merge, please make sure the following list is done and checked.
If an entry in not applicable, you can check it or remove it from the list.
- [x] Unless it's docs or a minor change: add [changelog](https://mailu.io/master/contributors/guide.html#changelog) entry file.
Co-authored-by: Wolfgang Jung <w.jung@polyas.de>
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