2498: Implement ITERATE in podop r=mergify[bot] a=nextgens
## What type of PR?
Feature
## What does this PR do?
This makes ``doveadm -A`` work.
The easiest way to try it out is:
```
doveadm dict iter proxy:/tmp/podop.socket:auth shared/userdb
or
doveadm user '*'
```
The protocol is described at https://doc.dovecot.org/developer_manual/design/dict_protocol/
The current version of dovecot is not using flags... so there's little gain in implementing them.
### Related issue(s)
- close#2499
## 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.
- [ ] 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>
Co-authored-by: Alexander Graf <ghostwheel42@users.noreply.github.com>