Consider adding "danger" feedback to MRs
Clarification and motivation
Currently reviewers have quite a few guidelines and rules to check for on open MRs in this project. These are mainly located in the guideline docs and in the MR template's checklist.
Some of them are already handled by CI already (e.g. trailing white-spaces), whereas others are conditional or optional.
For the latter kind, having a CI step for each (that's allowed to fail) would be mostly just distracting. A better solution to help with them would be having automated comments and warnings on MRs instead.
@Martoon suggested danger for this, that looks like a compelling choice, so we should give it a try.
Acceptance criteria
A danger
CI step with some rules is added to the project pipelines, unless different options are deemed better.