Merge #2790

2790: Implement managesieve support r=mergify[bot] a=nextgens

## What type of PR?

Feature

## What does this PR do?

This is a better a alternative to #2773

Expose managesieve to the outside world.

### Related issue(s)
- close #2773
- #428
- #113
- #81
- #1222

## Prerequisites
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] In case of feature or enhancement: documentation updated accordingly
- [x] Unless it's docs or a minor change: add [changelog](https://mailu.io/master/contributors/workflow.html#changelog) entry file.


Co-authored-by: Florent Daigniere <nextgens@freenetproject.org>

docs/compose/requirements.rst

@@ -63,7 +63,7 @@ address for your mail server and that you have a dedicated hostname
 with forward and reverse DNS entries for this IP address.
 
 Also, your host must not listen on ports ``25``, ``80``, ``110``, ``143``,
-``443``, ``465``, ``587``, ``993`` or ``995`` as these are used by Mailu
+``443``, ``465``, ``587``, ``993``, ``995`` nor ``4190`` as these are used by Mailu
 services. Therefore, you should disable or uninstall any program that is
 listening on these ports (or have them listen on a different port). For
 instance, on a default Debian install: