2705: Switch from docker.io to ghcr.io for deploying images r=nextgens a=Diman0
## What type of PR?
enhancement
## What does this PR do?
As we all know, docker has announced that they will stop with free docker organisations. The Mailu project used this. In about a month, the mailu docker org stops to exist and all images will be deleted.
This PR modifies the CI/CD workflow (github actions) to use ghcr.io as the container registry for deployed images. The images are first build with `-build` appended to the tag. These images are also used in the test step. Only in the deploy phase, are the final tags added (as it should be). This makes sure new images are only available after the deployment step.
The setup utility is updated to use `ghcr.io/mailu` as the docker_org.
All references to the docker org `mailu` have been replaced with `ghcr.io/mailu` in the documentation.
I confirmed via my Mailu_Fork repo that the github workflow works fine.
https://github.com/Diman0/Mailu_Fork/actions/runs/4440118095
### Related issue(s)
- closes#2704
## 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: Dimitri Huisman <diman@huisman.xyz>