This PR adds two new labels to interact with CI systems:
* `CI: Keep up to date` tells mergify bot to auto-update the PR against develop but do not merge it.
* `CI: No changelog needed` is meant to replace old `[ci no changelog needed]`
* `CI: Clean build required` marks PR as being incompatible with main development branch and will ensure that runners are cleaned before and after running jobs related to this PR.
Note that currently only first label is supported, others will follow with the build script update. However they need to be merged before, so I am able to develop and test them.