MWPSService currently uses the old pipeline lookup method. It searches
related merge requests with pipeline.ref, however, this doesn't work
for attached/detached merge request pipelines.
When a build fails for a commit, create a todo for the author of the
merge request that commit is the HEAD of. If the commit isn't the HEAD
commit of any MR, don't do anything. If there already is a todo for that
user and MR, don't do anything.
Current limitations:
- This isn't configurable by project.
- The author of a merge request might not be the person who pushed the
breaking commit.