Enable "Part-of:" commit message tagging in Marge bot
As part of only letting Marge run the CI (see gst-ci!274 (merged)) we need a way for Marge the merge bot to trigger a new pipeline under it's username. In Mesa, this always happens since Marge will rewrite all commit messages to add "Part-of:" tag, see mesa/mesa!4432 (commits) for an example).
I don't think this is a bad idea to have this tag, so basically I'm asking if we'd be ok with enabling that. I'd need @alatiera to take care of course.