2544: Fix#2242: Make quotas adjustable in 50MiB increments r=mergify[bot] a=nextgens
## What type of PR?
enhancement
## What does this PR do?
Make quotas adjustable in 50MiB increments
### Related issue(s)
- closes#2242
## 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>
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